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All answers having "Decreases" as clue:

4 Character Answers:

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EBBS



5 Character Answers:

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EASES

IRONS

SLOWS

WANES



6 Character Answers:

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TAPERS



7 Character Answers:

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LESSENS

LESSONS



8 Character Answers:

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DIESDOWN

SHORTENS



9 Character Answers:

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RAMPSDOWN