Meaning of “mug” - Learner’s Dictionary

mug

noun [ C ] uk us /mʌɡ/
CUP

A2 a large cup with straight sides usually used for hot drinks:

a coffee mug
a steaming mug of tea
PERSON informal

someone who is stupid and easily deceived:

I was such a mug to think he'd pay me back.

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