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All answers having "Diffuse" as clue:

4 Character Answers:

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SHED



5 Character Answers:

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EXUDE

IMBUE

STREW



6 Character Answers:

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OSMOSE



7 Character Answers:

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PERVADE

RADIATE



8 Character Answers:

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PERMEATE



11 Character Answers:

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BADTEMPERED

DISSEMINATE