In this answer about the non-word disabilitatedthis answer about the non-word disabilitated, the word preventative is compared (unfavourably, if my reading of the implication is correct) to preventive.
However, I have always used preventative, and can only recall hearing it in its longer form. Merriam-Webster online lists preventative (defining it as equal to preventive) as being first used circa 1666, and lists preventive as first used circa 1639.
Is this is a BrEng/AmEng difference? What is the etymology of these words?
(There is a question about this on World Wide Words, but more, or more precise, information would be appreciated.)