mid-15c., transitive, "turn (something) away, cause to turn away," from Old French avertir "turn, direct; avert; make aware" (12c.), from Vulgar Latin *advertire, from Latin avertere "to turn away; to drive away; shun; ward off; alienate," from ab "off, away from" (see ab-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend"). Meaning "ward off, prevent the occurrence of" is from 1610s. Related: Averted; averting.