The Collaborative International Dictionary of English v.0.48:
friendly fire \friend"ly fire`\, n. (Mil.) Weapons fire[9], such as artillery or aerial bombardment, from one's own forces; -- used mostly when troops do damage or cause casualties among their own forces; as, the tank was hit by friendly fire. [PJC]WordNet (r) 3.0 (2006):
friendly fire n 1: fire that injures or kills an ally [syn: friendly fire, fratricide]