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 (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.