loose cannon
Meaning
An unpredictable person who may cause trouble or damage, often by acting impulsively without considering consequences.
Origin
From naval warfare: a cannon that breaks loose on a ship can roll around and cause severe damage. By the 20th century it became a metaphor for a dangerously uncontrolled person.
Notes
Usually a negative label for a person whose unpredictability makes them risky to involve. Common in workplaces, politics, teams; suggests potential harm, not just “quirky.”
Examples
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He's a brilliant developer, but in meetings he's a loose cannon who can derail the whole discussion.
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The campaign worried that their spokesperson was a loose cannon and might say something offensive on live TV.
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If you put a loose cannon in charge of customer support, complaints will only get worse.
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The coach benched him because his temper made him a loose cannon on the field.
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We need a crisis plan in place—one loose cannon on social media can damage the brand overnight.
Grammar & Usage Notes
Typically used as a noun phrase: “a loose cannon,” “the loose cannon on the team.” Often with “be”: “He’s a loose cannon.” Sometimes expanded: “a loose cannon who…” Plural: “loose cannons.”
Synonyms
- wild card
- unpredictable person
- maverick
- liability
Antonyms
- safe pair of hands
- steady influence
- reliable person