1974, from French rétro (1973), supposedly first used of a revival c. 1968 of Eva Peron-inspired fashions and short for rétrograde (see retrograde). There is an isolated use in English from 1768, and the word apparently was used in 19c. French as a term in billiards. As a noun, short for retro-rocket (1948) from 1961.
word-forming element of Latin origin meaning "backwards; behind," from Latin retro (prep.) "backward, back, behind," usually in reference to place or position, rarely of time, "formerly, in the past," probably originally the ablative form of *reteros, based on re- "back" (see re-).
L. retro stands to re- as intro, "in, within"; to in, "in," and as citro, "hither," stands to cis, "on this side." [Klein]
Common in combinations in post-classical Latin (the classical equivalent was post-). Active in English as a word-forming element from mid-20c.
of powers, enactments, etc., "operating with respect to past circumstances, extending to matters which have occurred, holding good for preceding eases," from French rétroactif (16c.) "casting or relating back," from Latin retroact-, past-participle stem of retroagere "drive or turn back," from retro "back" (see retro-) + agere "to drive, set in motion" (from PIE root *ag- "to drive, draw out or forth, move"). Related: Retroactively; retroactivity.