Meaning

An unpredictable or reckless person, liable to cause havoc.

Origin

From 19th-century naval warfare, where a loose cannon-unsecured in a storm-smashed decks, deadly chaos noted in an 1850s log. By 1891, a 'Times' piece used it for an erratic MP.

Usage Examples

  • He's a loose cannon; might insult the client!
  • She's a loose cannon on stage; unscripted every night.
  • That loose cannon ruined the meeting with his rant.

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