Definition of “oath” - Learner’s Dictionary


noun uk us /əʊθ/

[ C ] a formal promise:

an oath of allegiance
They refused to take an oath of (= to promise) loyalty to the king.
under oath

If someone is under oath, they have promised to tell the truth in a law court:

He denied under oath that he was involved in the crime.

(Definition of “oath” from the Cambridge Learner's Dictionary © Cambridge University Press)