Etymology
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activity (n.)
c. 1400, "active or secular life," from Old French activité, from Medieval Latin activitatem (nominative activitas), a word in Scholastic philosophy, from Latin activus "active" (see active). Meaning "state of being active, briskness, liveliness" recorded from 1520s; that of "capacity for acting on matter" is from 1540s. As "an educational exercise," 1923.
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radioactive (adj.)

1898, of an atomic nucleus, "capable of spontaneous nuclear decay releasing ionizing emissions," from French radio-actif, coined by Pierre and Marie Curie from radio-, combining form of Latin radius "ray" (see radius) + actif "active" (see active). Of processes, etc., "involving or produced by radioactivity," by 1903.

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proactive (adj.)

also pro-active, of persons or policies, as an opposition to reactive, "taking the initiative in a situation, anticipating events" as opposed to responding to them, 1921, from pro- + active. From 1933, in psychology (learning theory). Related: Proactively; proactiveness; proactivity.

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*ag- 

Proto-Indo-European root meaning "to drive, draw out or forth, move."

It forms all or part of: act; action; active; actor; actual; actuary; actuate; agency; agenda; agent; agile; agitation; agony; ambagious; ambassador; ambiguous; anagogical; antagonize; apagoge; assay; Auriga; auto-da-fe; axiom; cache; castigate; coagulate; cogent; cogitation; counteract; demagogue; embassy; epact; essay; exact; exacta; examine; exigency; exiguous; fumigation; glucagon; hypnagogic; interact; intransigent; isagoge; litigate; litigation; mitigate; mystagogue; navigate; objurgate; pedagogue; plutogogue; prodigal; protagonist; purge; react; redact; retroactive; squat; strategy; synagogue; transact; transaction; variegate.

It is the hypothetical source of/evidence for its existence is provided by: Greek agein "to lead, guide, drive, carry off," agon "assembly, contest in the games," agōgos "leader," axios "worth, worthy, weighing as much;" Sanskrit ajati "drives," ajirah "moving, active;" Latin actus "a doing; a driving, impulse, a setting in motion; a part in a play;" agere "to set in motion, drive, drive forward," hence "to do, perform," agilis "nimble, quick;" Old Norse aka "to drive;" Middle Irish ag "battle."

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THC (n.)
active ingredient in marijuana and hashish, 1968, short for tetrahydrocannabinol (1940).
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spry (adj.)

1746, "active, nimble, vigorous, lively," dialectal, perhaps a shortening and alteration of sprightly [Barnhart], or from a Scandinavian source (compare Old Norse sprækr, dialectal Swedish sprygg "brisk, active"), from Proto-Germanic *sprek-, perhaps from PIE root *sper- "to spread, to sow" (see sparse).

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foe-man (n.)
also foeman, "active enemy," late Old English fah-man; see foe + man (n.).
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energetic (adj.)
1650s, "powerful in operation," from Greek energetikos "active," from energein "to work, be in action, act upon" (see energy). Of persons, "active," in English from 1796 (energetical "operative" is from c. 1600; from 1630s as "full of energy," while energical is attested from 1560s). Related: Energetically.
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bustling (adj.)
of a place, "noisily active," 1819, present-participle adjective from bustle (v.).
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rat-terrier (n.)

"small, active dog used to kill rats," by 1852, American English, from rat (n.) + terrier.

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