antacid (noun)
a substance that works against stomach acid
antibacterial (adjective)
designed to fight against or kill bacteria
antidote (noun)
a remedy or cure; something that works against a poison
antihistamine (noun)
a medicine that works against colds and allergies
antonym (noun)
a word that means the opposite of another word
retroactive (adjective)
goes back to a prior time
retrofit (verb)
to go back and install something that was not available at the time of original manufacturing
retrospective (adjective)
characterized by looking back at the past and reflecting; related to the past
retro, an, anti
backward, back against, opposite