Meaning of “deflate” - Learner’s Dictionary

deflate

verb uk us /dɪˈfleɪt/
LOSE AIR [ I, T ]

to let all the air or gas out of something, or to become emptied of air or gas:

to deflate a balloon/tyre
CONFIDENCE [ T ]

to make someone lose confidence or feel less important:

[ often passive ] They were totally deflated by losing the match.

(Definition of “deflate” from the Cambridge Learner’s Dictionary © Cambridge University Press)