1.  activity(n = noun.act) - any specific behavior; "they avoided all recreational activity"
is a kind of act, deed, human action, human activity
has particulars: variance, variation, space walk, domesticity, operation, operation, pattern, practice, diversion, recreation, bag, cup of tea, dish, follow-up, followup, game, play, turn, music, acting, performing, playacting, playing, animation, liveliness, burst, fit, work, deeds, works, service, business, job, line, line of work, occupation, occupation, committal to writing, writing, role, actus reus, misconduct, wrongdoing, wrongful conduct, dissipation, waste, wastefulness, attempt, effort, endeavor, endeavour, try, control, protection, sensory activity, didactics, education, educational activity, instruction, pedagogy, teaching, grooming, preparation, training, representation, creation, creative activity, disassembly, dismantlement, dismantling, puncture, hunt, hunting, search, employment, exercise, usage, use, utilisation, utilization, military operation, operation, measure, measurement, measuring, mensuration, calibration, standardisation, standardization, organisation, organization, grouping, support, supporting, continuance, continuation, procedure, process, ceremony, ceremony, worship, activating, activation, energizing, concealing, concealment, hiding, emplacement, locating, location, placement, position, positioning, provision, supply, supplying, demand, pleasure, delectation, enjoyment, lamentation, mourning, laughter, market, market place, marketplace, politics, preparation, readying, aid, assist, assistance, help, support, behavior, behaviour, conduct, doings, behavior, behaviour, leadership, leading, precedence, precedency, precession, solo, buzz, fun, hell, sin, outlet, release, vent, last, mystification, obfuscation, negotiation, verbalisation, verbalization, disturbance, perturbation, timekeeping
Antonym: inactivity
Derived forms adjective active₈, adjective active₄

2.  activity(n = noun.state) action, activeness - the state of being active; "his sphere of activity"; "he is out of action"
is a kind of state
has particulars: agency, busyness, hum, behavior, behaviour, eructation, eruption, extravasation, operation, overdrive, play, swing
Antonym: inactivity
Derived forms adjective active₁₄, adjective active₂

3.  activity(n = noun.process) bodily function, bodily process, body process - an organic process that takes place in the body; "respiratory activity"
is a kind of biological process, organic process
has particulars: control, breathing, external respiration, respiration, ventilation, respiration, breath, consumption, ingestion, intake, uptake, sex, sex activity, sexual activity, sexual practice, insemination, sleeping, reaction, response, crying, tears, weeping, ablactation, anastalsis, discharge, emission, expelling, expectoration, festering, maturation, suppuration, healing, hypostasis, lachrymation, lacrimation, tearing, watering, lactation, opsonisation, opsonization, overactivity, peristalsis, vermiculation, diaphoresis, hidrosis, perspiration, sudation, sweating, phagocytosis, pinocytosis, placentation, psilosis, tanning, transpiration
Derived form adjective active₁

4.  activity(n = noun.state) - (chemistry) the capacity of a substance to take part in a chemical reaction; "catalytic activity"
is a kind of capability, capacity
Derived form adjective active₆

5.  activity(n = noun.process) action, natural action, natural process - a process existing in or produced by nature (rather than by the intent of human beings); "the action of natural forces"; "volcanic activity"
is a kind of physical process, process
has particulars: radiation, absorption, acidification, adiabatic process, aeration, antiredeposition, capture, capture, centrifugation, chemical action, chemical change, chemical process, chromatography, concretion, condensation, convection, clotting, coagulation, curdling, decay, demagnetisation, demagnetization, desorption, diffusion, disintegration, dissolution, distillation, distillment, drift, effervescence, cataphoresis, dielectrolysis, electrophoresis, ionophoresis, ecesis, establishment, extinction, extraction, feedback, filtration, flocculation, flow, formation, fossilisation, fossilization, geologic process, geological process, curing, hardening, set, solidification, solidifying, inactivation, ion exchange, ionisation, ionization, leach, leaching, magnetic induction, magnetisation, magnetization, materialisation, materialization, nuclear reaction, opacification, oscillation, oxygenation, pair creation, pair formation, pair production, phase change, phase transition, physical change, state change, precession of the equinoxes, release, saltation, scattering, sericulture, sink, soak, soakage, soaking, softening, sorption, source, rigidification, rigidifying, stiffening, stimulation, ecological succession, succession, natural selection, selection, survival, survival of the fittest, synergism, synergy, temperature change, transduction, transpiration, vitrification
Derived forms adjective active₁₃, adjective active₉

6.  activity(n = noun.attribute) activeness - the trait of being active; moving or acting rapidly and energetically; "the level of activity declines with age"
is a kind of trait
has particulars: animation, brio, invigoration, spiritedness, vivification, dynamism, oomph, pizzaz, pizzazz, zing
Derived forms adjective active₅, adjective active₇, adjective active₃

   The state or quality of being active; nimbleness; agility; vigorous action or operation; energy; active force; as, an increasing variety of human activities. Palfrey. [1913 Webster]

activity, n. (pl. -ies)
1 a the condition of being active or moving about. b the exertion of energy; vigorous action.
2 (often in pl.) a particular occupation or pursuit (outdoor activities).
3 = RADIOACTIVITY.

Etymology:
F activit{eacute} or LL activitas (as ACTIVE)

N  activity, briskness, liveliness, animation, life, vivacity, spirit, dash, energy, snap, vim, nimbleness, agility, smartness, quickness, velocity, alacrity, promptitude, despatch, dispatch, expedition, haste, punctuality, eagerness, zeal, ardor, perfervidum aingenium, empressement, earnestness, intentness, abandon, vigor, devotion, exertion, industry, assiduity, assiduousness, sedulity, laboriousness, drudgery, painstaking, diligence, perseverance, indefatigation, habits of business, vigilance, wakefulness, sleeplessness, restlessness, insomnia, pervigilium, insomnium, racketing, movement, bustle, stir, fuss, ado, bother, pottering, fidget, fidgetiness, flurry, officiousness, dabbling, meddling, interference, interposition, intermeddling, tampering with, intrigue, press of business, no sinecure, plenty to do, many irons in the fire, great doings, busy hum of men, battle of life, thick of the action, housewife, busy bee, new brooms, sharp fellow, sharp blade, devotee, enthusiast, zealot, meddler, intermeddler, intriguer, busybody, pickthank, hummer, hustler, live man, rustler, active, brisk, brisk as a lark, brisk as a bee, lively, animated, vivacious, alive, alive and kicking, frisky, spirited, stirring, nimble, nimble as a squirrel, agile, light-footed, nimble-footed, featly, tripping, quick, prompt, yare, instant, ready, alert, spry, sharp, smart, fast, quick as a lamplighter, expeditious, awake, broad awake, go-ahead, live wide-awake, forward, eager, strenuous, zealous, enterprising, in earnest, resolute, industrious, assiduous, diligent, sedulous, notable, painstaking, intent, indefatigable, unwearied, unsleeping, never tired, plodding, hard-working, businesslike, workaday, bustling, restless, restless as a hyena, fussy, fidgety, pottering, busy, busy as hen with one chicken, working, at work, on duty, in harness, up in arms, on one's legs, at call, up and doing, up and stirring, busy, occupied, hard at work, hard at it, up to one's ears in, full of business, busy as a bee, busy as a one-armed paperhanger, meddling, meddlesome, pushing, officious, overofficious, intrigant, astir, stirring, agoing, afoot, on foot, in full swing, eventful, on the alert, actively, with life and spirit, with might and main &c, with haste, with wings, full tilt, in mediis rebus, Int, be alive, look alive, look sharp!, move on, push on!, keep moving!, go ahead!, stir your stumps!, age quod agis!, jaldi!, karo!, step lively!, carpe diem, seize the day, nulla dies sine linea, nec mora nec requies, the plot thickens, No sooner said than done, veni vidi vici, catch a weasel asleep, abends wird der Faule fleissig, dictum ac factum, schwere Arbeit in der Jugend ist sanfte Ruhe im Al, hard work in youth means soft rest in age, the busy hum of men.

N  energy, physical energy, force, power, keenness, intensity, vigor, strength, elasticity, go, high pressure, fire, rush, acrimony, acritude, causiticity, virulence, poignancy, harshness, severity, edge, point, pungency, cantharides, seasoning, activity, agitation, effervescence, ferment, fermentation, ebullition, splutter, perturbation, stir, bustle, voluntary energy, quicksilver, resolution, exertion, excitation, strong, energetic, forcible, active, intense, deep-dyed, severe, keen, vivid, sharp, acute, incisive, trenchant, brisk, rousing, irritation, poignant, virulent, caustic, corrosive, mordant, harsh, stringent, double-edged, double-shotted, double- distilled, drastic, escharotic, racy, potent, radioactive, strongly, fortiter in re, with telling effect, the steam is up, vires acquirit eundo, the race by vigor not by vaunts is won.

advanced research and development activity, agglutinating activity, bond-trading activity, business activity, commercial activity, creative activity, educational activity, extracurricular activity, government activity, human activity, intelligence activity, marine corps intelligence activity, offensive activity, optical activity, sensory activity, sex activity, sexual activity, social activity, spare-time activity, subversive activity