a person whose reckless behavior endangers the efforts or welfare of others.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
How to use loose cannon in a sentence
As for the wife, she is a loose cannon, willing to sacrifice the people close to her to get what she wants.
Cooper and Renner are solid as the loose cannon Richie and the upstanding Carmine, respectively.‘American Hustle’: A Sexy, Gleefully Chaotic Caper Starring Christian Bale and Jennifer Lawrence | Marlow Stern | December 10, 2013 | THE DAILY BEAST
Churchill, on the contrary, they regarded with alarm, a loose cannon, a rogue elephant.Bags of Swank: The Unlikely Alliance Between Churchill and George VI | Michael Korda | October 19, 2013 | THE DAILY BEAST
When Diana called for an international ban, seven months before she died, a Tory minister accused her of being a "loose cannon".
While some would be afraid to hire such a loose cannon, others see raw talent.Rebecca Martinson, the Viral Sorority Girl Letter Writer: How to Go From Unknown to Infamous in 60 Seconds | Tricia Romano | April 26, 2013 | THE DAILY BEAST
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
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
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.