It's rather crass to chime in with prescriptive comments on things that aren't nonstandard. They are both widely accepted as legitimate and wholly interchangeable, although it is true that some style guides still favor preventive.I must say I like the sound of this distinction, but in fact the two are interchangeable as both nouns and adjectives, though many prefer "preventive" as being shorter and simpler. "Preventative" used as an adjective dates back to the 17th century, as does "preventive" as a noun.