be witness to something

be (a) witness to (something)

1. To see something happen. Were there any witnesses to the accident?
2. To be proof of something. The many students on campus these days are a witness to the school's successful rebranding efforts.
See also: witness

be (a) ˈwitness to something

1 (formal) see something take place: He has been witness to a terrible murder.
2 (written) show that something is true; provide evidence for something: His good health is a witness to the success of the treatment.
See also: something, witness