early 15c., "to act in anticipation of," from L. præventus
, pp. of prævenire
"come before, anticipate, hinder," in L.L. also "to prevent," from præ
"before" + venire
"to come" (see venue
). Originally literal; sense of "anticipate to hinder" was in L., but not recorded in English until 1550s. Preventive
in the medical sense is recorded from 1640s.