loose cannon

English

Noun

loose cannon (plural loose cannons)

1. (nautical) a cannon that breaks loose during battle or a storm and causes serious damage to the ship and its crew
2. (idiomatic, by extension) an uncontrolled or unpredictable person who causes damage to their own faction, political party etc.

   Jack is considered a loose cannon due to his volatile personality and track record of demonstrating a lack of ability to maintain composure.

Verb

loose cannon (third-person singular simple present loose cannons, present participle loose cannoning, simple past and past participle loose cannoned)

1. (idiomatic) To behave in a way such as to cause damage to ones own faction, political party etc.
   • 2006, Gerry McCusker, Public Relations Disasters: Talespin--Inside Stories and Lessons Learnt, page 179,

     Gerald's loose cannoning triggered a volley of faithfully quoted media coverage which blasted a hole in his company's profits […] .