1. noun /ˈwɪt.nəs,ˈwɪt.nɪs/
She can bear witness, since she was there at the time.
As a witness to the event, I can tell you that he really said that.
2. verb /ˈwɪt.nəs,ˈwɪt.nɪs/
This certificate witnesses his presence on that day.
b) To take as evidence.
He witnessed the accident.
Wikipedia foundation.