Meaning of “vest” - Learner’s Dictionary

vest

noun [ C ] uk us /vest/
UNDERWEAR UK (US undershirt)

a piece of underwear that you wear under a shirt

WORN OVER A SHIRT US (UK waistcoat)

a piece of clothing with buttons at the front and no sleeves, that you wear over a shirt

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