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All answers having "Light up" as clue:

4 Character Answers:

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BEAM

GLOW

STAR



5 Character Answers:

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BLAZE

ELATE

GLEAM

SMOKE



6 Character Answers:

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IGNITE

ILLUME



8 Character Answers:

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ENKINDLE

ILLUMINE



9 Character Answers:

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IRRADIATE



10 Character Answers:

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ILLUMINATE