1.  To perceive or apprehend clearly and certainly; to understand; to have full information of; as, to know one's duty. [1913 Webster]
"O, that a man might know
The end of this day's business ere it come!" [1913 Webster]
"There is a certainty in the proposition, and we know it." [1913 Webster]
"Know how sublime a thing it is
To suffer and be strong." [1913 Webster]

2.  To be convinced of the truth of; to be fully assured of; as, to know things from information. [1913 Webster]

3.  To be acquainted with; to be no stranger to; to be more or less familiar with the person, character, etc., of; to possess experience of; as, to know an author; to know the rules of an organization. [1913 Webster]
"He hath made him to be sin for us, who knew no sin." [1913 Webster]
"Not to know me argues yourselves unknown." [1913 Webster]

4.  To recognize; to distinguish; to discern the character of; as, to know a person's face or figure. [1913 Webster]
"Ye shall know them by their fruits." [1913 Webster]
"And their eyes were opened, and they knew him." [1913 Webster]
"To know
Faithful friend from flattering foe." [1913 Webster]
"At nearer view he thought he knew the dead." [1913 Webster]

5.  To have sexual intercourse with. [1913 Webster]
" Know is often followed by an objective and an infinitive (with or without to) or a participle, a dependent sentence, etc." [1913 Webster]
"And Adam knew Eve his wife." [1913 Webster]
"And I knew that thou hearest me always." [1913 Webster]
"The monk he instantly knew to be the prior." [1913 Webster]
"In other hands I have known money do good." [1913 Webster]

1.  To have knowledge; to have a clear and certain perception; to possess wisdom, instruction, or information; -- often with of. [1913 Webster]
"Israel doth not know, my people doth not consider." [1913 Webster]
"If any man will do his will, he shall know of the doctrine, whether it be of God, or whether I speak of myself." [1913 Webster]
"The peasant folklore of Europe still knows of willows that bleed and weep and speak when hewn." [1913 Webster]

2.  To be assured; to feel confident. [1913 Webster]

know, v. & n.
--v. (past knew; past part. known)
1 tr. (often foll. by that, how, what, etc.) a have in the mind; have learnt; be able to recall (knows a lot about cars; knows what to do). b (also absol.) be aware of (a fact) (he knows I am waiting; I think he knows). c have a good command of (a subject or language) (knew German; knows his tables).
2 tr. be acquainted or friendly with (a person or thing).
3 tr. a recognize; identify (I knew him at once; knew him for an American). b (foll. by to + infin.) be aware of (a person or thing) as being or doing what is specified (knew them to be rogues). c (foll. by from) be able to distinguish (one from another) (did not know him from Adam).
4 tr. be subject to (her joy knew no bounds).
5 tr. have personal experience of (fear etc.).
6 tr. (as known adj.) a publicly acknowledged (a known thief; a known fact). b Math. (of a quantity etc.) having a value that can be stated.
7 intr. have understanding or knowledge.
8 tr. archaic have sexual intercourse with.
--n. (in phr. in the know) colloq. well-informed; having special knowledge.

Idiom:
all one knows (or knows how)
1 all one can (did all he knew to stop it).
2 adv. to the utmost of one's power (tried all she knew). before one knows where one is with baffling speed.
be not to know
1 have no way of learning (wasn't to know they'd arrive late).
2 be not to be told (she's not to know about the party). don't I know it! colloq. an expression of rueful assent. don't you know colloq. or joc. an expression used for emphasis (such a bore, don't you know). for all (or aught) I know so far as my knowledge extends. have been known to be known to have done (they have been known to not turn up). I knew it! I was sure that this would happen. I know what I have a new idea, suggestion, etc. know about have information about. know-all colloq. a person who seems to know everything. know best be or claim to be better informed etc. than others. know better than (foll. by that, or to + infin.) be wise, well-informed, or well-mannered enough to avoid (specified behaviour etc.).
know by name
1 have heard the name of.
2 be able to give the name of. know by sight recognize the appearance (only) of. know how know the way to do something.
know-how n.
1 practical knowledge; technique, expertise.
2 natural skill or invention. know-it-all = know-all.
know-nothing
1 an ignorant person.
2 an agnostic. know of be aware of; have heard of (not that I know of). know one's own mind be decisive, not vacillate. know the ropes (or one's stuff) be fully knowledgeable or experienced. know a thing or two be experienced or shrewd. know what's what have adequate knowledge of the world, life, etc. know who's who be aware of who or what each person is. not if I know it only against my will. not know that ... colloq. be fairly sure that ... not (I don't know that I want to go). not know what hit one be suddenly injured, killed, disconcerted, etc. not want to know refuse to take any notice of. what do you know (or know about that)? colloq. an expression of surprise.
you know colloq.
1 an expression implying something generally known or known to the hearer (you know, the pub on the corner).
2 an expression used as a gap-filler in conversation. you know something (or what)? I am going to tell you something. you-know-what (or -who) a thing or person unspecified but understood. you never know nothing in the future is certain.

Derivative:
knowable adj. knower n.

Etymology:
OE (ge)cnawan, rel. to CAN(1), KEN

VB  be friendly, be friends, be acquainted with, know, have the ear of, keep company with, hold communication with, have dealings with, sympathize with, have a leaning to, bear good will, love, make much of, befriend, introduce to, set one's horses together, have the latchstring out, hold out the right hand of friendship, extend the right hand of friendship, hold out the right hand of fellowship, become friendly, make friends with, break the lee, be introduced to, make acquaintance with, pick acquaintance with, scrape acquaintance with, get into favor, gain the friendship of, shake hands with, fraternize, embrace, receive with open arms, throw oneself into the arms of, meet halfway, take in good part.

VB  be sociable, know, be acquainted, associate with, sort with, keep company with, walk hand in hand with, eat off the same trencher, club together, consort, bear one company, join, make acquaintance with, make advances, fraternize, embrace, be at home with, feel at home with, make oneself at home with, make free with, crack a bottle with, receive hospitality, live at free quarters, find the latchstring out, visit, pay a visit, interchange visits, interchange cards, call at, call upon, leave a card, drop in, look in, look one up, beat up one's quarters, entertain, give a party, be at home, see one's friends, hang out, keep open house, do the honors, receive, receive with open arms, welcome, give a warm reception, to kill the fatted calf.

VB  be certain, stand to reason, render certain, insure, ensure, assure, clinch, make sure, determine, decide, set at rest, make assurance double sure, know, dogmatize, lay down the law.

VB  believe, credit, give faith to, give credit to, credence to, see, realize, assume, receive, set down for, take for, have it, take it, consider, esteem, presume, count upon, depend upon, calculate upon, pin one's faith upon, reckon upon, lean upon, build upon, rely upon, rest upon, lay one's account for, make sure of, make oneself easy about, on that score, take on trust, take on credit, take for granted, take for gospel, allow some weight to, attach some weight to, know, know for certain, have know, make no doubt, doubt not, be, rest assured, persuade oneself, assure oneself, satisfy oneself, make up one's mind, give one credit for, confide in, believe in, put one's trust in, place in, repose in, implicit confidence in, take one's word for, at one's word, place reliance on, rely upon, swear by, regard to, think, hold, take, take it, opine, be of opinion, conceive, trow, ween, fancy, apprehend, have it, hold a belief, possess, entertain a belief, adopt a belief, imbibe a belief, embrace a belief, get hold of a belief, hazard, foster, nurture a belief, cherish a belief, have an opinion, hold an opinion, possess, entertain an opinion, adopt an opinion, imbibe an opinion, embrace an opinion, get hold of an opinion, hazard an opinion, foster an opinion, nurture an opinion, cherish an opinion, view as, consider as, take as, hold as, conceive as, regard as, esteem as, deem as, look upon as, account as, set down as, surmise, get it into one's head, take it into one's head, come round to an opinion, swallow, cause to be believed, satisfy, persuade, have the ear of, gain the confidence of, assure, convince, convict, convert, wean, bring round, bring over, win over, indoctrinate, cram down the throat, produce conviction, carry conviction, bring home to, drive home to, go down, find credence, pass current, be received, be current, possess, take hold of, take possession of the mind.

VB  know, ken, scan, wot, wot aware, be aware of, ween, weet, trow, have, possess, conceive, apprehend, comprehend, take, realize, understand, savvy, appreciate, fathom, make out, recognize, discern, perceive, see, get a sight-of, experience, know full well, have some knowledge of, possess some knowledge of, be au courant, have in one's head, have at one' fingers ends, know by heart, know by rote, be master of, connaitre le dessous des cartes, know what's what, see one's way, discover, come to one's knowledge.

VB  tell, inform, inform of, acquaint, acquaint with, impart, impart to, make acquaintance with, apprise, advise, enlighten, awaken, transmit, let fall, mention, express, intimate, represent, communicate, make known, publish, notify, signify, specify, convey the knowledge of, let one know, have one to know, give one to understand, give notice, set before, lay before, put before, point out, put into one's head, put one in possession of, instruct, direct the attention to, announce, annunciate, report, report progress, bringword, send word, leave word, write word, telegraph, telephone, wire, retail, render an account, give an account, state, let slip, blurt out, spill the beans, unburden oneself of, let off one's chest, disclose, show cause, explain, hint, given an inkling of, give a hint, drop a hint, throw out a hint, insinuate, allude to, make allusion to, glance at, tip the wink, suggest, prompt, give the cue, breathe, whisper, whisper in the ear, give a bit of one's mind, tell one plainly, tell once for all, speak volumes, undeceive, unbeguile, set right, correct, open the eyes of, disabuse, disillusion one of, be informed of, know, learn, get scent of, get wind of, gather from, awaken to, open one's eyes to, become alive, become awake to, hear, overhear, understand, come to one's ears, come to one's knowledge, reach one's ears.

desire to know, in the know, know all the answers, know apart, know backwards and forwards, know how, know no bounds, know nothing, know the score, know well, know what's going on, know what's what, royal society of london for improving natural know