loose cannon
noun
a person whose reckless behavior endangers the efforts or welfare of others.
Origin of loose cannon
First recorded in 1975–80
Words nearby loose cannon
looping,
looping mill,
loopy,
loos,
loose,
loose cannon,
loose change,
loose cover,
loose end,
loose ends,
loose forward
British Dictionary definitions for loose cannon
loose cannon
noun
a person or thing that appears to be beyond control and is potentially a source of unintentional damage
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.