Originally (like grotesque) a 16c. Italian word referring to the strange and fantastic representations on ancient murals unearthed around Rome (especially the Baths of Titus, rediscovered 16c.); later extended to "any bizarre thing or behavior," in which sense it first arrived in English. As an adjective in English from 1580s, "grotesque, bizarre." In 17c. the spelling antique was restricted to the original sense of that word.
1530s, "aged, venerable;" 1540s, "having existed in ancient times," from French antique "old" (14c.), from Latin antiquus (later anticus) "ancient, former, of olden times; old, long in existence, aged; venerable; old-fashioned," from PIE *anti- "before" (from root *ant- "front, forehead," with derivatives meaning "in front of, before") + *okw- "to see."
Originally pronounced in English like its doublet antic, but French pronunciation and spelling were adopted in English from c. 1700. The meaning "not modern" is from 1640s. Related: Antiqueness.
It forms all or part of: advance; advantage; along; ancestor; ancient (adj.); answer; Antaeus; ante; ante-; ante meridiem; antecede; antecedent; antedate; antediluvian; ante-partum; antepenultimate; anterior; anti-; antic; anticipate; anticipation; antique; antler; avant-garde; elope; end; rampart; un- (2) prefix of reversal; until; vambrace; vamp (n.1) "upper of a shoe or boot;" vanguard.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit antah "end, border, boundary;" Hittite hanti "opposite;" Greek anta, anten "opposite," anti "over against, opposite, before;" Latin ante (prep., adv.) "before (in place or time), in front of, against;" Old Lithuanian anta "on to;" Gothic anda "along;" Old English and- "against;" German ent- "along, against."