(nautical) A cannon that breaks loose from its moorings on a ship during battle or storm, which has the potential to cause serious damage to the ship and her crew.

(idiomatic) To behave in a way such as to cause damage to one's own faction, political party, etc.

simple past tense and past participle of loose cannon

Third-person singular simple present indicative form of loose cannon

plural of loose cannon

present participle of loose cannon