Definition of witness :
1. Attestation of a fact or an event; testimony.
2. One who is cognizant; a person who beholds, or otherwise has personal knowledge of, anything; as, an eyewitness; an earwitness.
3. One who sees the execution of an instrument, and subscribes it for the purpose of confirming its authenticity by his testimony; one who witnesses a will, a deed, a marriage, or the like.
4. One who testifies in a cause, or gives evidence before a judicial tribunal; as, the witness in court agreed in all essential facts.
5. That which furnishes evidence or proof.
6. To bear testimony; to give evidence; to testify.
7. To give testimony to; to testify to; to attest.
8. To see or know by personal presence; to have direct cognizance of.
9. To see the execution of, as an instrument, and subscribe it for the purpose of establishing its authenticity; as, to witness a bond or a deed.
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evince (part of speech: verb)
betoken, document, determine, evince, demonstrate, prove, corroborate, exemplify, establish, indicate, substantiate, connote, validate, observe, adduce, illustrate, certify, vouch, manifest, confirm, avouch, attest, state, support, exhibit, testify, declare, authenticate, depose
see (part of speech: verb)
spectator (part of speech: noun)
observe (part of speech: verb)