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All answers having "Guiding principle" as clue:

3 Character Answers:

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LAW

RHO



5 Character Answers:

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CREDO

CREED

ETHIC

MOTTO

POLES

TENET



7 Character Answers:

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PRECEPT



8 Character Answers:

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LOADSTAR

POLESTAR



10 Character Answers:

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GOLDENRULE