WITNESS

1. one who gives evidence in a cause before a court and who attests or swears to facts or gives testimony under oath; 2. to observe the execution of, as that of an instrument, or to sign one's name to it to authenticate it (attest it). ADVERSE [HOSTILE] WITNESS: one whose relationship to the opposing party is such that his or her testimony may be prejudiced against that party.
CHARACTER WITNESS: a witness who testifies at another person's trial, vouching for that person's high moral character and standing in the community, but who does not have knowledge of the validity of the charges against that person. EXAMPLE: The preacher testified as a character witness at Brian's rial, giving many examples of Brian's service to the elderly and poor. Looking only at the charitable work Brian had done, the preacher could not believe Brian would burglarize a house.
EXPERT WITNESS: see expert witness.
HOSTILE WITNESS: see ADVERSE [HOSTILE] WITNESS.
LAY WITNESS: see lay witness.
MATERIAL WITNESS: one who can give testimony that might have a bearing upon the outcome of a cause and that no one else is able to give. In criminal law, the term refers particularly to a witness about whom there is reasonable expectation that he or she can give testimony bearing upon the defendant's guilt or innocence.
Source: Barron's Dictionary of Legal Terms, Steven H. Gifis, 5th Edition; © 2016