late 14c., auncyen, of persons, "very old;" c. 1400, of things, "having lasted from a remote period," from Old French ancien "old, long-standing, ancient," from Vulgar Latin *anteanus, literally "from before," adjectivization of Latin ante "before, in front of, against" (from PIE *anti "against," locative singular of root *ant- "front, forehead"). The unetymological -t dates from 15c. by influence of words in -ent.
From early 15c. as "existing or occurring in times long past." Specifically, in history, "belonging to the period before the fall of the Western Roman Empire" (c. 1600, contrasted with medieval and modern). In English law, "from before the Norman Conquest." As a noun, "very old person," late 14c.; "one who lived in former ages," 1530s. Ancient of Days "supreme being" is from Daniel vii.9. Related: Anciently.
"standard-bearer," 1590s, short for ancient-bearer (1570s), from ancient "flag, banner, standard" (1550s), a corruption of ensign (q.v.). Archaic, but preserved in Shakespeare's character Aunchient Pistoll in "Henry V."