The Etymology of Preventive and Preventative
Around 1635, someone had the idea of adding the -ive suffix to the verb prevent. Around the same time, preventative evolved as a variant spelling.
When was the word preventative first used?
The word "preventive" first saw use in 1602, appearing as the older English form "preuentiue" (imagine the U's as V's when you're trying to pronounce it - it's still weird).
When did preventive become preventative?
History of Preventative and Preventive
Of the two, preventive is slightly older, appearing in English at the beginning of the 17th century.
