What is Witness?
Witness is (noun) 1. a person who sees something happen or who is present when something happens The witness happened to be outside the house when it was burgled. 2. a person who appears before a court or committee to give evidence Her sister appeared as a witness in the libel case. 3. a person who is present when someone signs a document The contract has to be signed in front of two witnesses. His sister signed as a witness. 4. to bear witness to to be evidence that something is true (formal.) His reaction bore witness to his interest in the matter. (verb) 1. to be present when something happens, and see it happening Did anyone witness the accident? 2. to sign a document to show that you guarantee that the other signatures on it are genuine One of his colleagues witnessed his signature.
source: Easier English, Student Dictionary Upper Intermediate Level