loose cannon

See synonyms for loose cannon on Thesaurus.com
  1. a person whose reckless behavior endangers the efforts or welfare of others.

Origin of loose cannon

First recorded in 1975–80

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use loose cannon in a sentence

  • A man reached the head of the ladder, stepped upon one of the loose cannon-balls and fell with an oath and a crash.

    Lysbeth | H. Rider Haggard

British Dictionary definitions for loose cannon

loose cannon

  1. a person or thing that appears to be beyond control and is potentially a source of unintentional damage

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Other Idioms and Phrases with loose cannon

loose cannon

One who is uncontrolled and therefore a serious and unpredictable danger. For example, We can't trust her to talk to the press—she's a loose cannon. This metaphoric expression alludes to cannon mounted on the deck of a sailing ship, which if dislodged during combat or a storm could cause serious damage to both vessel and crew by sliding about. Its figurative use dates from the first half of the 1900s.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.