Definition of "Witness" :

noun: testimony by word or deed to your religious faith

noun: a close observer; someone who looks at something (such as an exhibition of some kind)

noun: someone who sees an event and reports what happened

noun: (law) a person who attests to the genuineness of a document or signature by adding their own signature

noun: (law) a person who testifies under oath in a court of law

verb: be a witness to

"She witnessed the accident and had to testify in court."

verb: perceive or be contemporaneous with