Meaning of “witness” - Learner’s Dictionary

witness

verb [ T ] uk us /ˈwɪtnəs/
SEE

B2 to see something happen, especially an accident or crime:

Did anyone witness the attack?
DOCUMENT

to sign your name on an official document to say that you were present when someone else signed it

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