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All answers having "Caustic" as clue:

3 Character Answers:

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LYE



4 Character Answers:

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ACID

SHUT

TART



5 Character Answers:

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ACERB

ACRID

HARSH

SHARP

SNIDE



6 Character Answers:

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BITING



7 Character Answers:

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ERODENT

EROSIVE

MORDANT

SATIRIC



8 Character Answers:

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STRIDENT



9 Character Answers:

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ACIDULOUS

CORRODENT

CORROSIVE

RECTITUDE

SATIRICAL



11 Character Answers:

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ACRIMONIOUS