"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.
late 14c., "vital force in plants and animals;" early 15c., "act of creating or making," from Old French formacion "formation, fashioning, creation" (12c.) or directly from Latin formationem (nominative formatio) "a forming, shaping," noun of action or condition from past-participle stem of formare "to form," from forma "form, shape" (see form (n.)). Meaning that which is formed or created" is from 1640s. In geology, "group of rocks having a similar origin or character," 1815. Related: Formational.
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Harper, D. (n.d.). Etymology of back-formation. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/back-formation