What is Adverse Witness?

Legal Definition
A witness who gives negative evidence against the party who called them as a witness. Refer to hostile witness.
Legal Definition
A witness whose mind discloses a bias hostile to the party examining him; not a witness whose evidence, being honestly given, is adverse to the case of the examinant. Brown; Greenough v. Eccles, 5 O. B. (N. S.) 801.
-- Black's Law Dictionary