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All answers having "Vernacular" as clue:

5 Character Answers:

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ARGOT

IDIOM

LINGO

SLANG



6 Character Answers:

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JARGON

PATOIS



7 Character Answers:

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DEMOTIC

DIALECT



8 Character Answers:

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PARLANCE



9 Character Answers:

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IDIOMATIC



10 Character Answers:

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COLLOQUIAL