Definition of: witness

(wit′nis) noun
1. An act or fact of attestation to a fact or an event; testimony; evidence.
2. A person who has seen or knows something, and is therefore competent to give evidence concerning it; a spectator.
3. That which serves as or furnishes evidence or proof.
4. Law One who has knowledge of facts relating to a given cause and is subpoenaed to testify; also, a person who has signed his name to an instrument executed by another in order that he may testify to the genuineness of the maker's signature. See synonyms under SPECTATOR, TESTIMONY.
—v.t.
1. To see or know by personal experience.
2. To furnish or serve as evidence of.
3. To give testimony to.
4. To be the site or scene of: This spot has witnessed many heinous crimes.
5. Law To see the execution of (an instrument) and subscribe to it for the purpose of establishing its authenticity.
—v.i.
6. To give evidence; testify. See synonyms under AVOW. [OE witnes knowledge, testimony]
—wit′ness·er noun