early 15c., preventen, "act in anticipation of, act sooner or more quickly than (another)," from Latin praeventus, past participle of praevenire "come before, anticipate, hinder," in Late Latin also "to prevent," from prae "before" (see pre-) + venire "to come" (from a suffixed form of PIE root *gwa- "to go, come").
Originally in the literal classical meaning. The meaning "keep from existing or occurring" is by 1540s; the sense of "anticipate to hinder, hinder from action by opposition of obstacles" was in Latin but is not recorded in English until 1660s.
"serving to prevent or hinder; guarding against or warding off," 1630s, from Latin praevent-, past-participle stem of praevenire "come or go before, anticipate" (see prevent), + -ive. As a noun, "something taken or done beforehand," from 1630s; in medical use from 1670s. Related: Preventively; preventiveness.
Others are reading
Definitions of preventative from WordNet
remedy that prevents or slows the course of an illness or disease;