Online Etymology Dictionary

possibly (adv.): c. 1400, from possible (adj.) + -ly (2).
POSSLQ: 1979, acronym from person of opposite sex sharing living quarters; it never was an official category.
possum (n.): 1610s, shortened form of opossum. Phrase play possum is first recorded 1822.
post (n.1): "a timber set upright," from Old English post "pillar, doorpost," and Old French post "post, upright beam," both from Latin postis "door, post, doorpost," perhaps from por- "forth" (see pro-) + stare "to stand," from PIE root *stā- "to stand, set down, make or be firm" (see stet).

Similar compounds are Sanskrit prstham "back, roof, peak," Avestan parshti "back," Greek pastas "porch in front of a house, colonnade," Middle High German virst "ridepole," Lithuanian pirstas, Old Church Slavonic pristu "finger" (PIE *por-st-i-).
post (n.2): "place when on duty," 1590s, from Middle French poste "place where one is stationed," also, "station for post horses" (16c.), from Italian posto "post, station," from Vulgar Latin *postum, from Latin positum, neuter past participle of ponere "to place, to put" (see position (n.)). Earliest sense in English was military; meaning "job, position" is attested 1690s.
post (n.3): "mail system," c. 1500, "riders and horses posted at intervals," from post (n.2) on notion of riders and horses "posted" at intervals along a route to speed mail in relays, probably formed on model of Middle French poste in this sense (late 15c.). Meaning "system for carrying mail" is from 1660s.
post (v.4): "to put up bail money," 1781, from one of the nouns post, but which one is uncertain. Related: Posted; posting.
post (v.1): "to affix (a paper, etc.) to a post" (in a public place), hence, "to make known," 1630s, from post (n.1). Related: Posted; posting.
post (v.2): in bookkeeping, "to transfer from a day book to a formal account," 1620s, from post (n.2) via a figurative sense of "carrying" by post horses. Related: Posted; posting.
post (v.3): "to send through the postal system," 1837, from post (n.3). Earlier, "to travel with relays of horses" (1530s). Related: Posted; posting.
post (v.5): "to station at a post," from post (n.2). Related: Posted; posting.
post (adv.): 1540s, "with post horses," hence, "rapidly;" especially in the phrase to ride post "go rapidly," from post (n.3).
post factum: Latin, literally "after the fact," from factum "deed, act" (see fact).
post hoc: Latin, "after this." Especially in post hoc, ergo propter hoc, logical fallacy, literally "after this, therefore because of this."
post meridiem: "after noon," 1640s, Latin, from post "after" (see post-) + accusative of meridies (see meridian).
post office (n.): 1650s, "public department in charge of letter-carrying," from post (n.3) + office. Meaning "building where postal business is carried on" is from 1650s. In slang or euphemistic sense of "a sexual game" it refers to an actual parlor game first attested early 1850s in which pretend "letters" were paid for by kisses.
post restante: direction on mail that it be held at that post office until called for, French, literally "remaining post."
post-: word-forming element meaning "after," from Latin post "behind, after, afterward," from *pos-ti (source also of Arcadian pos, Doric poti "toward, to, near, close by;" Old Church Slavonic po "behind, after," pozdu "late;" Lithuanian pas "at, by"), from PIE *apo- (source also of Greek apo "from," Latin ab "away from" see apo-).
post-bellum (adj.): also postbellum, used in U.S. South from 1874 in reference to American Civil War; see post- + bellicose.
post-classical (adj.): 1845, from post- + classical.
post-glacial (adj.): 1855, from post- + glacial.
post-graduate (adj.): also postgraduate, 1858, originally American English, from post- + graduate (adj.). As a noun, attested from 1890. Abbreviation post-grad is recorded from 1950.
post-hole (n.): 1703, from post (n.1) + hole (n.).
post-impressionism (n.): 1910, from post- + impressionism.
Post-it (n.): 1975, proprietary name.
post-millennial (adj.): also postmillennial, 1831, from post- "after" + millennial; chiefly in reference to the Protestant doctrine that the second coming of Christ will occur after, not at, the Christian millennium.
post-modern (adj.): also post-modern, post modern, by 1919, in frequent use from 1949, from post- + modern.
But it has been only during the later decades of the modern era -- during that time interval that might fairly be called the post-modern era -- that this mechanistic conception of things has begun seriously to affect the current system of knowledge and belief; and it has not hitherto seriously taken effect except in technology and in the material sciences. [Thorstein Veblen, "The Vested Interests and the Common Man," 1919]

So much for the misapplied theory which has helped set the artist's nerves a-quiver and incited him to the extremes of post modern art, literary and other. [Wilson Follett, "Literature and Bad Nerves," "Harper's," June 1921]
Of architecture from 1940s; specific sense in the arts emerged 1960s (see postmodernism).
post-mortem (adj.): also postmortem, 1734 (adverb), from Latin post mortem, from post "after" (see post-) + mortem, accusative of mors "death" (see mortal (adj.)). From 1835 as an adjective. As a noun, shortening of post-mortem examination, it is recorded from 1850.
post-operative (adj.): also postoperative, "occurring after a surgical operation," 1869, from post- + operative. Short form post-op is attested from 1971.
post-partum (adj.): also postpartum, 1837, "occurring after birth," from Latin post partum "after birth," from post "after" (see post-) + accusative of partus "a bearing, a bringing forth," from partus, past participle of parere "to bring forth" (see pare). Phrase Post-partum depression first attested 1929.
postage (n.): 1580s, "sending of mail by post;" 1650s as "cost of sending something by mail," from post (n.3) + -age. Postage stamp is attested from 1840; they were recorded as being collected in albums by 1862.
postal (adj.): "pertaining to the mail system," 1843, on model of French postale (1836), from post (n.3). Noun meaning "state of irrational and violent anger" (usually in phrase going postal) attested by 1997, in reference to a cluster of news-making workplace shootings in U.S. by what were commonly described as "disgruntled postal workers" (the cliche itself, though not the phrase, goes back at least to 1994).
postcard (n.): 1870, from post (n.3) + card (n).
postdate (v.): also post-date, 1620s, from post- + date (v.1) "to assign a date to, to mark a date on." Related: Postdated; postdating. Intransitive meaning "be of an earlier date" is from 1909.
postdiluvial (adj.): also post-diluvial, 1823, from post- + diluvial. Earlier was postdiluvian (1670s).
posted (adj.): "supplied with news," 1828, American English, past participle adjective from post (v.2).
poster (n.): "bill, placard, thing posted," 1838, from post (v.1). Poster boy/girl/child "someone given prominence in certain causes" is attested by 1990, in reference to fund-raising drives for charities associated with disability, featuring child sufferers, a feature since 1930s.
posterior (adj.): 1530s, "later," from Latin posterior "after, later, behind," comparative of posterus "coming after, subsequent," from post "after" (see post-). Meaning "situated behind" is from 1630s.
posterior (n.): "buttocks," euphemistic, 1610s, from posterior (adj.). Earlier it meant "those who come after, posterity" (1530s). Compare Lithuanian pasturas "the last, the hindmost," from pas "at, by."
posteriority (n.): late 14c., "state of being behind," from Old French posteriorite (Modern French postériorité), from Medieval Latin posterioritatem (nominative posterioritas), from Latin posterior "later" (see posterior (adj.)).
posterity (n.): late 14c., from Old French posterité (14c.), from Latin posteritatem (nominative posteritas) "future, future time; after-generation, offspring;" literally "the condition of coming after," from posterus "coming after, subsequent," from post "after" (see post-). Old English words for this included æftercneoreso, framcynn.
postern (n.): late 13c., "back door, private door," from Old French posterne "side or rear gate," earlier posterle, from Late Latin posterula "small back door or gate," diminutive of Latin posterus "that is behind, coming after, subsequent," from post "after" (see post-).
posthaste (adv.): 1590s, from a noun (1530s) meaning "great speed," usually said to be from "post haste" instruction formerly written on letters (attested from 1530s), from post (adv.) + haste (n.). The verb post "to ride or travel with great speed" is recorded from 1550s.
posthumous (adj.): mid-15c., "born after the death of the originator" (author or father), from Late Latin posthumus, from Latin postumus "last, last-born," superlative of posterus "coming after, subsequent" (see posterior). Altered in Late Latin by association with Latin humare "to bury," suggesting death; the one born after the father's death obviously being the last. An Old English word for this was æfterboren, literally "after-born." Related: Posthumously.
postillon (n.): 1590s, from Middle French postillon (1530s), from Italian postiglione "forerunner, guide," especially for one carrying mail on horseback, from posta "mail" (see post (n.3)) + compound suffix from Latin -ilio.
postlude (n.): 1821, from post- + ending abstracted from prelude.
postman (n.): 1520s, from post (n.3) + man (n.).
postmark (n.): 1670s, from post (n.3) + mark (n.1). As a verb from 1716. Related: Postmarked; postmarking.
postmaster (n.): 1510s, from post (n.3) + master (n.).
postmodernism (n.): also post-modernism, by 1977, from post- + modernism. Defined by Terry Eagleton as "the contemporary movement of thought which rejects ... the possibility of objective knowledge" and is therefore "skeptical of truth, unity, and progress" ["After Theory," 2003]. Related: post-modernist (1965).