they have, of course, a good many senses; of interest to us are these

de- In a bad sense, so as to put down or subject to some indignity: as decipere to take in, deceive; deludere to make game of, delude; deridere to laugh to scorn, deride; detesteri to abominate, detest.

il- (used like in-, before l) in this case, in the sense of (to play) on, upon or against