preventive/preventative: Common Errors in English Usage Entry for Wednesday, May 9, 2012.

preventive/preventative
It is sometimes argued that “preventive” is the adjective, “preventative” the noun. 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.