When suggesting to writers that they use preventive rather than preventative, some will argue with me by saying that if preventative is in the dictionary, then it's a word.
The argument should not be over whether a word is in the dictionary. Starting with vulgarities, we wouldn't use many words appearing in the dictionary. So the argument should be whether a word is acceptable in your company or industry. I just found preventative in Oxford, Merriam-Webster, and Dictionary.com, but they all preferred preventive. The simpler word will nearly always be the better choice.
