Meaning of “witness” - Learner’s Dictionary

witness

noun [ C ] uk us /ˈwɪtnəs/
COURT

someone in a court of law who says what they have seen and what they know about a crime:

The witness was called to the stand.
SEE

B2 someone who sees an accident or crime:

Police are appealing for witnesses to the shooting.
DOCUMENT

someone who signs their name on an official document to say that they were present when someone else signed it

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