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All answers having "Swells" as clue:

4 Character Answers:

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FOPS

SEAS



5 Character Answers:

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GROWS

RISES



6 Character Answers:

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ADDSTO

BLOATS

SURGES



7 Character Answers:

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DILATES

EXPANDS

PUFFSUP



8 Character Answers:

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DISTENDS

ENGORGES

ENLARGES