Paul "The Pride of Cornell" Wolfowitz, in a comment on the recently squashed plan to offer trading in terrorism futures, seemed to this tin ear to have used the word imaginive. Googling turns up only 22 hits, so it may have been a case of Wolfy mushmouth, but it got me wondering about the -at- in imaginative vs. the -at- in preventative. Why does the one belong and the other not? AHD on-line is not too helpful, giving etymologies for neither imaginative nor preventive. Any ideas?