loose cannon

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a person whose reckless behavior endangers the efforts or welfare of others.
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Origin of loose cannon

First recorded in 1975–80
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does loose cannon mean?

A loose cannon is someone who behaves unpredictably and recklessly, often in a way that puts others at risk or negatively affects what they’re trying to do.

People considered loose cannons can’t be trusted because there’s no telling what they’re going to say or do. Loose cannons are thought to be uncontrollable. The metaphor is based on the image of a cannon on a ship that comes loose (such as during a storm) and starts dangerously sliding around and slamming into the people on board and the parts of the ship, causing injuries and damage.

Example: I need everyone on my team to be on the same page and to work together—I don’t want any loose cannons causing chaos.

Where does loose cannon come from?

he first records of the phrase loose cannon come from before the 1900s. The metaphor dates back to the time when wooden warships used to carry cannons, which were tied down to prevent them from shifting around as the ship moved. These cannons were big and heavy, and one coming loose would be very dangerous (mostly due to smashing into people and things, as opposed to exploding).

The phrase loose cannon is usually applied to the person in a group or on a team who’s unpredictable and whose unpredictability is likely to cause some kind of damage. Their recklessness may make it difficult for the team to accomplish its task, or it may derail the effort altogether. This recklessness can come in the form of erratic behavior, or it may come in the form of the incendiary things the loose cannon says.

The figurative sense of time bomb can refer to a person who’s likely to “explode” and cause some kind of chaos or damage. However, it’s most commonly used to refer to situations, as opposed to people. The figurative sense of powder keg is similar, but it always refers to potentially explosive situations.

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What are some words that share a root or word element with loose cannon


What are some words that often get used in discussing loose cannon?

How is loose cannon used in real life?

Calling someone a loose cannon is almost always intended as a criticism.



Try using loose cannon!

Which of the following words does NOT describe someone who’s considered a loose cannon?

A. dangerous
B. reckless
C. predictable
D. erratic

How to use loose cannon in a sentence

British Dictionary definitions for loose cannon

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

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.