Antonyms are words that have opposite meanings to another word. The antonyms for "pre-requisite" are words that describe something that is not needed or required before something else. One antonym for "pre-requisite" is "optional," which means something that may be chosen but is not essential. Another antonym is "unimportant," which refers to something of little or no significance. A third antonym for "pre-requisite" is "unnecessary," which means something that is not required or needed at all. Other possible antonyms include "secondary," "additional," and "supplementary," all of which suggest something that is not crucial or essential.