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All answers having "More shrewd" as clue:

5 Character Answers:

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CUTER

SAGER

SLIER

SLYER

WISER



6 Character Answers:

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CAGIER

FOXIER



7 Character Answers:

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ASTUTER

CANNIER

HEADIER



8 Character Answers:

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CLEVERER



9 Character Answers:

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OTHERWISE