Wiktionary
n. (context legal English) In a legal trial, a person called to testify as a witness by a party to whom that witness is opposed.
WordNet
n. a witness whose relationship to the opposing party is such that his or her testimony may be prejudiced against the opposing party; "a hostile witness can be asked leading questions and cross-examined" [syn: adverse witness]
Wikipedia
Hostile Witness is a 1968 British courtroom-based drama film based on a play by Jack Roffey, directed by Ray Milland (who had starred in the play on Broadway) and starring Milland, Sylvia Sims, Raymond Huntley and Julian Holloway.
Usage examples of "hostile witness".
All I need to do is to put Harris on the stand, let him tell his story, call her to the stand and let it appear she's a hostile witness.
Which means he's two seconds away from arresting you and putting you on display as a hostile witness, then releasing you and letting Sam Giancana or whoever have you killed.
If subpoenaed, I will be a hostile witness and stand on the Fifth Amendment, and I am prepared to go to prison for contempt of court.
We had the brooding presence of Verovolcus -no longer the comic figure, but a hostile witness whose knowledge of these mad Roman machinations could do us great harm.
No explanation had been offered for this terrible assault, and the complainant had appeared involuntarily before the Grand jury and afterward had to be kept in the House of Detention as a hostile witness.