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All answers having "Impassive" as clue:

4 Character Answers:

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PAIN



5 Character Answers:

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COMMA

STOIC

STONY



6 Character Answers:

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OUTCRY

STOLID

WOODEN



7 Character Answers:

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DRYEYED

STOICAL



9 Character Answers:

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UNPITYING



10 Character Answers:

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PHLEGMATIC



11 Character Answers:

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EMOTIONLESS