Loose cannon

Someone who is unpredictable and can cause damage if not kept in check.

From the 17th century to the 19th century, wooden warships carried cannon as their primary offensive weapons. In order to avoid damage from their enormous recoil when fired they were mounted on rollers and secured with rope. A loose cannon was just what it sounds like, that is, a cannon that had become free of its restraints and was rolling dangerously about the deck.

Ex: He’s a bit of a loose cannon, he could do anything at any time, too much of a liability if you ask me.



Spanish: bomba de relojería



German: tickende Zeitbombe