feedback n.

Old English fedan "nourish, give food to, sustain, foster" (transitive), from Proto-Germanic *fodjan (source also of Old Saxon fodjan, Old Frisian feda, Dutch voeden, Old High German fuotan, Old Norse foeða, Gothic fodjan "to feed"), from PIE root *pa- "to feed." Intransitive sense "take food, eat" is from late 14c. Meaning "to supply to as food" is from 1818.

"to or toward the rear or the original starting place; in the past; behind in position," literally or figuratively, late 14c., shortened from abak, from Old English on bæc "backwards, behind, aback" (see back (n.), and compare aback). To give (something) back is to give it again, to give it in the opposite direction to that in which it was formerly given. Adverbial phrase back and forth is attested by 1814.

also bio-feedback, "use of electronics to monitor an automatic bodily function to train a person to control it," 1969, from bio- + feedback. Said to have been coined by U.S. psychologist and parapsychologist Gardner Murphy.