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All answers having "Tremble" as clue:

5 Character Answers:

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COWER

QUAKE

SHAKE



6 Character Answers:

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DODDER

QUAVER

QUIVER

SHIVER



7 Character Answers:

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FLUTTER

SHUDDER

VIBRATE



9 Character Answers:

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ASTRONAUT

PALPITATE



14 Character Answers:

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SHAKELIKEALEAF