Merriam-Webster Collegiate Dictionary - witness

 I. noun  Etymology: Middle English ~e, from Old English witnes knowledge, testimony, ~, from 2wit  Date: before 12th century  1. attestation of a fact or event ; testimony  2. one that gives evidence; specifically one who testifies in a cause or before a judicial tribunal  3. one asked to be present at a transaction so as to be able to testify to its having taken place  4. one who has personal knowledge of something  5.  a. something serving as evidence or proof ; sign  b. public affirmation by word or example of usually religious faith or conviction the heroic ~ to divine life — Pilot  6. capitalized a member of the Jehovah's Witnesses  II. verb  Date: 14th century  transitive verb  1. to testify to ; attest  2. to act as legal ~ of  3. to furnish proof of ; betoken  4.  a. to have personal or direct cognizance of ; see for oneself ~ed the historic event  b. to take note of our grammar— ~ our verb system—is a marvel of flexibility, variety, and exactitude — Charlton Laird  5. to constitute the scene or time of structures…which this striking Dorset hilltop once ~ed — Times Literary Supplement  intransitive verb  1. to bear ~ ; testify  2. to bear ~ to one's religious convictions opportunity to ~ for Christ — Billy Graham  Synonyms: see certify