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All answers having "Building block" as clue:

4 Character Answers:

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ATOM

JEER

LEGO

UNIT



5 Character Answers:

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ADOBE

AMINO

BRICK



6 Character Answers:

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CINDER

CSTONE

PLINTH



7 Character Answers:

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ONEACRE



8 Character Answers:

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MEGALITH



11 Character Answers:

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CORNERSTONE