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All answers having "Tighten" as clue:

4 Character Answers:

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EDIT

FLEX

GIRD

LACE



5 Character Answers:

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RETIE



6 Character Answers:

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CLENCH

LACEUP

RELACE

RESEAL



7 Character Answers:

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TENSEUP



9 Character Answers:

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CONSTRICT