| a person whose reckless behavior endangers the efforts or welfare of others. |
| loose cannon n. Slang One that is uncontrolled and therefore poses danger: "[His] bloopers in the White House seem to make him . . . a political loose cannon" (Tom Morgenthau). [From the threat posed by loose cannon rolling about a warship under sail.] |
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.