1.  A stroke or blow. [1913 Webster]
"Curse on that cross, quoth then the Sarazin,
That keeps thy body from the bitter fit." [1913 Webster]

2.  A sudden and violent attack of a disorder; a stroke of disease, as of epilepsy or apoplexy, which produces convulsions or unconsciousness; a convulsion; a paroxysm; hence, a period of exacerbation of a disease; in general, an attack of disease; as, a fit of sickness. [1913 Webster]
"And when the fit was on him, I did mark
How he did shake." [1913 Webster]

3.  A mood of any kind which masters or possesses one for a time; a temporary, absorbing affection; a paroxysm; as, a fit of melancholy, of passion, or of laughter. [1913 Webster]
"All fits of pleasure we balanced by an equal degree of pain." [1913 Webster]
"The English, however, were on this subject prone to fits of jealously." [1913 Webster]

4.  A passing humor; a caprice; a sudden and unusual effort, activity, or motion, followed by relaxation or inaction; an impulsive and irregular action. [1913 Webster]
"The fits of the season." [1913 Webster]

5.  A darting point; a sudden emission. [1913 Webster]
"A tongue of light, a fit of flame." [1913 Webster]

fit, adj., v., n., & adv.
--adj. (fitter, fittest)
1 a (usu. foll. by for, or to + infin.) well adapted or suited. b (foll. by to + infin.) qualified, competent, worthy. c (foll. by for, or to + infin.) in a suitable condition, ready. d (foll. by for) good enough (a dinner fit for a king). e (foll. by to + infin.) sufficiently exhausted, troubled, or angry (fit to drop).
2 in good health or athletic condition.
3 proper, becoming, right (it is fit that).
--v. (fitted, fitting)
1 a tr. (also absol.) be of the right shape and size for (the dress fits her; the key doesn't fit the lock; these shoes don't fit). b tr. make, fix, or insert (a thing) so that it is of the right size or shape (fitted shelves in the alcoves). c intr. (often foll. by in, into) (of a component) be correctly positioned (that bit fits here). d tr. find room for (can't fit another person on the bench).
2 tr. (foll. by for, or to + infin.) a make suitable; adapt. b make competent (fitted him to be a priest).
3 tr. (usu. foll. by with) supply, furnish (fitted the boat with a new rudder).
4 tr. fix in place (fit a lock on the door).
5 tr. = fit on.
6 tr. be in harmony with, befit, become (it fits the occasion; the punishment fits the crime).
--n. the way in which a garment, component, etc., fits (a bad fit; a tight fit).
--adv. (foll. by to + infin.) colloq. in a suitable manner, appropriately (was laughing fit to bust).

Idiom:
fit the bill = fill the bill. fit in
1 (often foll. by with) be (esp. socially) compatible or accommodating (doesn't fit in with the rest of the group; tried to fit in with their plans).
2 find space or time for (an object, engagement, etc.) (the dentist fitted me in at the last minute). fit on try on (a garment). fit out (or up) (often foll. by with) equip. fit-up Theatr.
sl.
1 a temporary stage etc.
2 a travelling company. see (or think) fit (often foll. by to + infin.) decide or choose (a specified course of action).

Derivative:
fitly adv. fitness n.

fit, n.
1 a sudden seizure of epilepsy, hysteria, apoplexy, fainting, or paralysis, with unconsciousness or convulsions.
2 a sudden brief attack of an illness or of symptoms (fit of coughing).
3 a sudden short bout or burst (fit of energy; fit of giggles).
4 colloq. an attack of strong feeling (fit of rage).
5 a capricious impulse; a mood (when the fit was on him).

Idiom:
by (or in) fits and starts spasmodically. give a person a fit colloq. surprise or outrage him or her. have a fit colloq. be greatly surprised or outraged. in fits laughing uncontrollably.

fit, n. (also fytte) archaic a section of a poem.

Etymology:
OE fitt

N  caprice, fancy, humor, whim, whimsy, whimsey, whimwham, crotchet, capriccio, quirk, freak, maggot, fad, vagary, prank, fit, flimflam, escapade, boutade, wild-goose chase, capriciousness, kink, capricious, erratic, eccentric, fitful, hysterical, full of whims, maggoty, inconsistent, fanciful, fantastic, whimsical, crotchety, kinky, particular, humorsome, freakish, skittish, wanton, wayward, contrary, captious, arbitrary, unconformable, penny wise and pound foolish, fickle, frivolous, sleeveless, giddy, volatile, by fits and starts, without rhyme or reason, nil fuit unquain sic inipar sibi, the deuce is in him.

N  state, condition, category, estate, lot, ease, trim, mood, pickle, plight, temper, aspect, dilemma, pass, predicament, constitution, habitude, diathesis, frame, fabric, stamp, set, fit, mold, mould, mode, modality, schesis, form, tone, tenor, turn, trim, guise, fashion, light, complexion, style, character, conditional, modal, formal, structural, organic, conditionally, as the matter stands, as things are, such being the case.

N  expedience, expediency, desirableness, desirability, fitness, utility, propriety, opportunism, advantage, high time, expedient, desirable, advisable, acceptable, convenient, worth while, meet, fit, fitting, due, proper, eligible, seemly, becoming, befitting, opportune, in loco, suitable, applicable, in the right place, conveniently, operae pretium est.

VB  be accordant, agree, accord, harmonize, correspond, tally, respond, meet, suit, fit, befit, do, adapt itself to, fall in with, chime in with, square with, quadrate with, consort with, comport with, dovetail, assimilate, fit like a glove, fit to a tittle, fit to a T, match, become one, homologate, consent, render accordant, fit, suit, adapt, accommodate, graduate, adjust, dress, regulate, readjust, accord, harmonize, reconcile, fadge, dovetail, square, be accordant, agree, accord, harmonize, correspond, tally, respond, meet, suit, fit, befit, do, adapt itself to, fall in with, chime in with, square with, quadrate with, consort with, comport with, dovetail, assimilate, fit like a glove, fit to a tittle, fit to a T, match, become one, homologate, consent, render accordant, fit, suit, adapt, accommodate, graduate, adjust, dress, regulate, readjust, accord, harmonize, reconcile, fadge, dovetail, square.

VB  be equal, equal, match, reach, keep pace with, run abreast, come to, amount to, come up to, be on a level with, lie on a level with, balance, cope with, come to the same thing, render equal, equalize level, dress, balance, equate, handicap, give points, spot points, handicap, trim, adjust, poise, fit, accommodate, adapt, strike a balance, establish equality, restore equality, restore equilibrium, readjust, stretch on the bed of Procrustes.

N  disease, illness, sickness, ailing, all the ills that flesh is heir to, morbidity, morbosity, infirmity, ailment, indisposition, complaint, disorder, malady, distemper, distemperature, visitation, attack, seizure, stroke, fit, delicacy, loss of health, invalidation, cachexy, cachexia, atrophy, marasmus, indigestion, dyspepsia, decay, decline, consumption, palsy, paralysis, prostration, taint, pollution, infection, sepsis, septicity, infestation, epidemic, pandemic, endemic, epizootic, murrain, plague, pestilence, pox, sore, ulcer, abscess, fester, boil, pimple, wen, carbuncle, gathering, imposthume, peccant humor, issue, rot, canker, cold sore, fever sore, cancer, carcinoma, leukemia, neoplastic disease, malignancy, tumor, caries, mortification, corruption, gangrene, sphacelus, sphacelation, leprosy, eruption, rash, breaking out, fever, temperature, calenture, inflammation, ague, angina pectoris, appendicitis, Asiatic cholera, spasmodic cholera, biliary calculus, kidney stone, black death, bubonic plague, pneumonic plague, blennorrhagia, blennorrhoea, blood poisoning, bloodstroke, bloody flux, brash, breakbone fever, dengue fever, malarial fever, Q-fever, heart attack, cardiac arrest, cardiomyopathy, hardening of the arteries, arteriosclerosis, atherosclerosis, bronchocele, canker rash, cardialgia, carditis, endocarditis, cholera, asphyxia, chlorosis, chorea, cynanche, dartre, enanthem, enanthema, erysipelas, exanthem, exanthema, gallstone, goiter, gonorrhea, green sickness, grip, grippe, influenza, flu, hay fever, heartburn, heaves, rupture, hernia, hemorrhoids, piles, herpes, itch, king's evil, lockjaw, measles, mumps, polio, necrosis, pertussis, phthisis, pneumonia, psora, pyaemia, pyrosis, quinsy, rachitis, ringworm, rubeola, St. Vitus's dance, scabies, scarlatina, scarlet fever, scrofula, seasickness, struma, syntexis, tetanus, tetter, tonsillitis, tonsilitis, tracheocele, trachoma, trismus, varicella, varicosis, variola, water qualm, whooping cough, yellow fever, yellow jack, fatal disease, dangerous illness, galloping consumption, churchyard cough, general breaking up, break up of the system, idiocy insanity, martyr to disease, cripple, the halt the lame and the blind, valetudinary, valetudinarian, invalid, patient, case, sickroom, sick- chamber, pathology, etiology, nosology, anthrax, bighead, blackleg, blackquarter, cattle plague, glanders, mange, scrapie, milk sickness, heartworm, feline leukemia, roundworms, quarter-evil, quarter-ill, rinderpest, virus, bacterium, bacteria, DNA virus, RNA virus, rhinovirus, rhabdovirus, picornavirus, herpesvirus, cytomegalovirus, CMV, human immunodefficiency virus, HIV, diseased, ailing, ill, ill of, taken ill, seized with, indisposed, unwell, sick, squeamish, poorly, seedy, affected with illness, afflicted with illness, laid up, confined, bedridden, invalided, in hospital, on the sick list, out of health, out of sorts, under the weather, valetudinary, unsound, unhealthy, sickly, morbid, morbose, healthless, infirm, chlorotic, unbraced, drooping, flagging, lame, crippled, halting, morbid, tainted, vitiated, peccant, contaminated, poisoned, tabid, mangy, leprous, cankered, rotten, rotten to the core, rotten at the core, withered, palsied, paralytic, dyspeptic, luetic, pneumonic, pulmonic, phthisic, rachitic, syntectic, syntectical, tabetic, varicose, touched in the wind, broken-winded, spavined, gasping, hors de combat, weakly, weakened, decrepit, decayed, incurable, in declining health, cranky, in a bad way, in danger, prostrate, moribund, morbific epidemic, endemic, zymotic.

N  excitability, impetuosity, vehemence, boisterousness, turbulence, impatience, intolerance, nonendurance, irritability, itching, wincing, disquiet, disquietude, restlessness, fidgets, fidgetiness, agitation, trepidation, perturbation, ruffle, hurry, fuss, flurry, fluster, flutter, pother, stew, ferment, whirl, buck fever, hurry-skurry, thrill, state of excitement, fever of excitement, transport, passion, excitement, flush, heat, fever, heat, fire, flame, fume, blood boiling, tumult, effervescence, ebullition, boiling over, whiff, gust, story, tempest, scene, breaking out, burst, fit, paroxysm, explosion, outbreak, outburst, agony, violence, fierceness, rage, fury, furor, furore, desperation, madness, distraction, raving, delirium, phrensy, frenzy, hysterics, intoxication, tearing passion, raging passion, anger, fascination, infatuation, fanaticism, Quixotism, Quixotry, tete montee, excitable, easily excited, in an excitable state, high-strung, irritable, impatient, intolerant, feverish, febrile, hysterical, delirious, mad, moody, maggoty- headed, unquiet, mercurial, electric, galvanic, hasty, hurried, restless, fidgety, fussy, chafing, startlish, mettlesome, high-mettled, skittish, vehement, demonstrative, violent, wild, furious, fierce, fiery, hot-headed, madcap, overzealous, enthusiastic, impassioned, fanatical, rabid, rampant, clamorous, uproarious, turbulent, tempestuous, tumultuary, boisterous, impulsive, impetuous, passionate, uncontrolled, uncontrollable, ungovernable, irrepressible, stanchless, inextinguishable, burning, simmering, volcanic, ready to burst forth, volatile, excited, exciting, Int, pish!, pshaw!, noli me tangere, filled with fury, rapt, inspir'd, maggiore fretta minore atto.

N  violence, inclemency, vehemence, might, impetuosity, boisterousness, effervescence, ebullition, turbulence, bluster, uproar, callithump, riot, row, rumpus, le diable a quatre, devil to pay, all the fat in the fire, severity, ferocity, rage, fury, exacerbation, exasperation, malignity, fit, paroxysm, orgasm, climax, aphrodisia, force, brute force, outrage, coup de main, strain, shock, shog, spasm, convulsion, throe, hysterics, passion, outbreak, outburst, debacle, burst, bounce, dissilience, discharge, volley, explosion, blow up, blast, detonation, rush, eruption, displosion, torrent, turmoil, ferment, storm, tempest, rough weather, squall, earthquake, volcano, thunderstorm, berserk, berserker, fury, dragon, demon, tiger, beldame, Tisiphone, Megaera, Alecto, madcap, wild beast, fire eater, violent, vehement, warm, acute, sharp, rough, rude, ungentle, bluff, boisterous, wild, brusque, abrupt, waspish, impetuous, rampant, turbulent, disorderly, blustering, raging, troublous, riotous, tumultuary, tumultuous, obstreperous, uproarious, extravagant, unmitigated, ravening, inextinguishable, tameless, frenzied, desperate, infuriate, furious, outrageous, frantic, hysteric, in hysterics, fiery, flaming, scorching, hot, red-hot, ebullient, savage, fierce, ferocious, fierce as a tiger, excited, unquelled, unquenched, unextinguished, unrepressed, unbridled, unruly, headstrong, ungovernable, unappeasable, immitigable, unmitigable, uncontrollable, incontrollable, insuppressible, irrepressible, orgastic, orgasmatic, orgasmic, spasmodic, convulsive, explosive, detonating, volcanic, meteoric, stormy, violently, amain, by storm, by force, by main force, with might and main, tooth and nail, vi et armis, at the point of the sword, at the point of the bayonet, at one fell swoop, with a high hand, through thick and thin, in desperation, with a vengeance, a outrance, a toute outrance, headlong, head foremost, furor arma ministrat, blown with restless violence round about the pende.

N  resentment, displeasure, animosity, anger, wrath, indignation, exasperation, bitter resentment, wrathful indignation, pique, umbrage, huff, miff, soreness, dudgeon, acerbity, virulence, bitterness, acrimony, asperity, spleen, gall, heart-burning, heart-swelling, rankling, ill humor, bad humor, ill temper, bad temper, irascibility, ill blood, revenge, excitement, irritation, warmth, bile, choler, ire, fume, pucker, dander, ferment, ebullition, towering passion, acharnement, angry mood, taking, pet, tiff, passion, fit, tantrums, burst, explosion, paroxysm, storm, rage, fury, desperation, violence, fire and fury, vials of wrath, gnashing of teeth, hot blood, high words, scowl, sulks, affront, provocation, offense, indignity, grudge, crow to pluck, bone to pick, sore subject, casus belli, ill turn, outrage, Furies, Eumenides, buffet, slap in the face, box on the ear, rap on the knuckles, angry, wrath, irate, ireful, wrathful, cross, Achillean, sulky, bitter, virulent, acrimonious &c (discourteous), violent, warm, burning, boiling, boiling over, fuming, raging, foaming, foaming at the mouth, convulsed with rage, offended, waxy, acharne, wrought, worked up, indignant, hurt, sore, set against, fierce, wild, rageful, furious, mad with rage, fiery, infuriate, rabid, savage, relentless, flushed with anger, flushed with rage, in a huff, in a stew, in a fume, in a pucker, in a passion, in a rage, in a fury, in a taking, in a way, on one's high ropes, up in arms, in high dudgeon, angrily, in the height of passion, in the heat of passion, in the heat of the moment, Int, tantaene animis coelestibus irae!, marry come up!, zounds!, 'sdeath!, one's blood being up, one's back being up, one's monkey being up, fervens difficili bile jecur, the gorge rising, eyes flashing fire, the blood rising, the blood boiling, haeret lateri lethalis arundo, beware the fury of a patient man, furor arma ministrat, ira furor brevis est, quem Jupiter vult perdere dementat prius, What, drunk with choler?.

N  right, what ought to be, what should be, fitness, summum jus, justice, equity, equitableness, propriety, fair play, impartiality, measure for measure, give and take, lex talionis, Astraea, Nemesis, Themis, scales of justice, evenhanded justice, karma, suum cuique, clear stage, fair field and no favor, level playing field, morals, law, honor, virtue, right, good, just, reasonable, fit, equal, equable, equatable, evenhanded, fair, legitimate, justifiable, rightful, as it should be, as it ought to be, lawful deserved, rightly, +a bon droit, au bon droit, in justice, in equity, in reason, without distinction of persons, without regard to persons, without respect to persons, upon even terms, Int, all right!, fair's fair, Dieu et mon droit, in equal scale weighing delight and dole, justitia cuum cuique distribuit, justitiae soror incorrupta fides, justitia virtutem regina, thrice is he armed that hath his quarrel just.

N  due, dueness, right, privilege, prerogative, prescription, title, claim, pretension, demand, birthright, immunity, license, liberty, franchise, vested interest, vested right, sanction, authority, warranty, charter, warrant, constitution, tenure, bond, claimant, appellant, plaintiff, having a right to, entitled to, claiming, deserving, meriting, worthy of, privileged, allowed, sanctioned, warranted, authorized, ordained, prescribed, constitutional, chartered, enfranchised, prescriptive, presumptive, absolute, indefeasible, unalienable, inalienable, imprescriptible, inviolable, unimpeachable, unchallenged, sacrosanct, due to, merited, deserved, condign, richly deserved, allowable, lawful, licit, legitimate, legal, legalized, square, unexceptionable, right, equitable, due, en r gle, fit, fitting, correct, proper, meet, befitting, becoming, seemly, decorous, creditable, up to the mark, right as a trivet, just the thing, quite the thing, selon les r gles, duly, ex officio, de jure, by right, by divine right, jure divino, Dei gratia, in the name of, civis Romanus sum, +a chaque saint sa chandelle.

fit in, fit out, fit the bill, fit to be tied, have a fit, see fit, throw a fit