1580s, "a tilting or turning backward," noun of action or state from Latin retroversus "turned or bent backwards," from retro "back" (see retro-) + versus "turned toward or against," past participle of vertere "to turn, turn back, be turned; convert, transform, translate; be changed" (from PIE root *wer- (2) "to turn, bend").
"bent backward," 1776, in botany, from Modern Latin retroflexus, past participle of retroflectere "to bend back," from retro "back" (see retro-) + flectere "to bend" (see flexible). The verb "to turn or fold back" (1898) is a back-formation from retroflexed (1806), which is from the adjective. Related: Retroflexion.
late 14c., of planets, "appearing to move in the sky contrary to the usual direction," from Latin retrogradus "going back, moving backward," from retrogradi "move backward," from retro "backward, reverse" (see retro-) + gradi "to go, step" (from PIE root *ghredh- "to walk, go"). General sense of "tending to revert" is recorded from 1530s; that of "directed backward, in a direction contrary to the original motion" is from 1620s. .
"balance due, that which is behind in payment," early 15c., plural noun from Middle English arrere (adv.) "in or to the rear; in the past; at a disadvantage" (c. 1300), from Anglo-French arrere, Old French ariere "behind, backward" (12c., Modern French arrière), from Vulgar Latin *ad retro, from Latin ad "to" (see ad-) + retro "behind" (see retro-).
It generally implies that part of the money already has been paid. Arrearage (early 14c.) was the earlier noun. Phrase in arrears first recorded 1610s, but in arrearages is from late 14c.
"hindmost part, the space behind or at the back," c. 1600, abstracted from rerewarde "rear guard, hindmost part of an army or fleet" (mid-14c.), from Anglo-French rerewarde, Old French rieregarde, from the Old French adverb riere "behind" (from Latin retro "back, behind;" see retro-) + Old French garde "guardian" (see guard (n.)).
Earliest use often is specifically military, "hindmost body of an army or fleet." The English word in many early examples also may be a shortened form of arrear (see arrears), perhaps a misdivision of the arrears.
As a euphemism for "buttocks" it is attested by 1796. As an adverb, "behind," early 15c. As an adjective, "hindmost; pertaining to or situated in the rear," c. 1300, from Old French rere.
To bring up the rear "come last in order" is from 1640s. The naval rank of rear admiral is attested from 1580s, said to be so called from his originally ranking "behind" an admiral proper. Rear-view (mirror) is recorded from 1926. Rear-supper (c. 1300) was an old name for "last meal of the day."
"move backward; deteriorate," 1816, probably a back-formation from retrogression. Related: Retrogressed; retrogressing.
"turned up (of the nose), pug," 1802, from French (nez) retroussé (16c.), past-participle adjective from retrousser "to turn up."