retro (adj.)

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. .