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All answers having "Good-bye" as clue:

4 Character Answers:

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CIAO

TATA



5 Character Answers:

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ADIEU

ADIOS



6 Character Answers:

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PLIERS

SEEYOU

SOLONG



7 Character Answers:

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CHEERIO

MRCHIPS



8 Character Answers:

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EIGHTEEN

ENDANGER

FAREWELL



12 Character Answers:

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SEEYOUAROUND



15 Character Answers:

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TILLWEMEETAGAIN