Set of principles central to credo suiting the faith concept (5)

I believe the answer is:

ethic

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'set of principles' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for ethic that I've seen before include "Set of moral principles" , "Code of principles" , "An unusual factor in morals" , "Moral system" , "Ideology" .)

I've seen this clue in The Times.

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