Antonyms for "pumps up" include "deflates," "reduces," "depresses," "flattens," and "shrinks." When something is "pumped up," it is usually inflating, increasing or enhancing, so its antonyms are the opposite. For example, if you "pump up" a balloon, its antonym would be "deflate," meaning to reduce or let out air from the balloon. If someone "pumps up" their ego or confidence, the antonyms would be "depress" or "shrink" since those words mean to lower or decrease one's self-esteem. Knowing the antonyms of a word helps to understand its full range of meaning and how it can be used in different contexts.