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All answers having "Lose one's cool" as clue:

4 Character Answers:

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FLIP

SNAP



5 Character Answers:

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ERUPT

GOAPE

PANIC



6 Character Answers:

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GONUTS

SEERED



8 Character Answers:

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HAVEAFIT



9 Character Answers:

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BLOWAFUSE

THROWAFIT



11 Character Answers:

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BLOWAGASKET



15 Character Answers:

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FLYOFFTHEHANDLE