loose cannon

noun

1. a person whose reckless behavior endangers the efforts or welfare of others.

loose cannon

noun

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

Word History and Origins

Origin of loose cannon¹

First recorded in 1975–80

Idioms and Phrases

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.

Example Sentences

As for the wife, she is a loose cannon, willing to sacrifice the people close to her to get what she wants.

From The Daily Beast

Cooper and Renner are solid as the loose cannon Richie and the upstanding Carmine, respectively.

From The Daily Beast

Churchill, on the contrary, they regarded with alarm, a loose cannon, a rogue elephant.

From 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".

From The Daily Beast

While some would be afraid to hire such a loose cannon, others see raw talent.

From 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.

From Project Gutenberg