late 15c., absurdite, "that which is absurd," from Late Latin absurditatem (nominative absurditas) "dissonance, incongruity," noun of state from Latin absurdus "out of tune;" figuratively "incongruous, silly, senseless" (see absurd).

late 15c., "that which is heaped up, an accumulated mass," from Latin accumulationem (nominative accumulatio) "a heaping up," noun of action from past-participle stem of accumulare "to heap up, amass," from ad "to," here perhaps emphatic (see ad-), + cumulare "heap up," from cumulus "heap" (from suffixed form of PIE root *keue- "to swell"). Meaning "act of heaping up" is from c. 1600.

late 15c., "made customary, habitual, often practiced or used," past-participle adjective from accustom (v.).

late 15c., "act of completing" (something), from French achèvement "a finishing," noun of action from Old French achever "to finish, accomplish" (see achieve). Meaning "thing achieved" is recorded from 1590s.

late 15c., "admit or show one's knowledge," a blend of Middle English aknow "admit or show one's knowledge" and Middle English knowlechen "admit, acknowledge" (c. 1200; see knowledge). Middle English aknow is from Old English oncnawan "understand, come to recognize," from on (see on (prep.)) + cnawan "recognize;" see know).

"By 16th c. the earlier vbs. knowledge and a(c)know ... were obs., and acknowledge took their place" [OED]. In the merger, an unetymological -c- slipped in; perhaps the explanation is that when English kn- became a simple "n" sound, the -c- stepped up to preserve, in this word, the ancient "kn-" sound. Related: Acknowledged; acknowledging.

late 15c., "one who plays at games of chance," agent noun from adventure (v.). The meaning "one who undertakes commercial ventures" is from c. 1600. The meaning "one who seeks adventures" is from 1660s. It often is used in a bad sense, "seeker of fortune by rash or underhanded means;" hence adventurism (1843, in early 20c. a term in communist jargon). Fem. form adventuress attested by 1754.

late 15c., "informed;" 1780s, "publicly announced," past-participle adjective from advertise.

"readiness to be sociable or to converse," late 15c., from Old French affabilité (14c.), noun of quality from affable (see affable).

of persons, "open to conversation or approach," late 15c., from Old French affable "benign, approachable" (14c.), from Latin affabilis "approachable, courteous, kind, friendly," literally "who can be (easily) spoken to," from affari "to speak to," from ad "to" (see ad-) + fari "to speak" (from PIE root *bha- (2) "to speak, tell, say"). Related: Affably. Glossed in Old English as wordwynsum.

late 15c., "one who acts," from Latin agentem (nominative agens) "effective, powerful," present participle of agere "to set in motion, drive forward; to do, perform; keep in movement" (from PIE root *ag- "to drive, draw out or forth, move").

The meaning "any natural force or substance which produces a phenomenon" is from 1550s. The meaning "deputy, representative" is from 1590s. The sense of "spy, secret agent" is attested by 1916.