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All answers having "Discovered" as clue:

3 Character Answers:

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SAW



4 Character Answers:

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SEEN



5 Character Answers:

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FOUND

GOTAT

LITON

SPIED



6 Character Answers:

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CLOSET

ESPIED

LEARNT



7 Character Answers:

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ECHELON

LEARNED

SIGHTED



8 Character Answers:

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CAMEUPON

DETECTED

FOUNDOUT

REALISED



9 Character Answers:

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LEARNEDOF

UNEARTHED



11 Character Answers:

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ASCERTAINED