wit·ness

– verb
1. to see, hear, or know by personal presence and perception.
2. to be present at (an occurrence) as a spectator or bystander, etc.
3. to attest by one's signature.
4. testify; give or afford evidence.
– noun
5. an individual who, being present, personally sees or perceives a thing; a beholder or spectator.
6. a person or thing that affords evidence.
7. a person who gives testimony.
8. a person who signs a document attesting the genuineness of its execution.