Meaning of “underestimate” - Learner’s Dictionary

underestimate

verb [ T ] uk us /ˌʌndərˈestɪmeɪt/
SIZE/AMOUNT

B2 to not understand how large, strong, or important something is:

Many people underestimate the cost of owning a car.
PERSON

to not understand how powerful or clever someone is:

I thought it would be an easy game but I had underestimated my opponent.
→ Opposite overestimate

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