Possibly St Thomas’s fundamental values (5)

I believe the answer is:

'fundamental values' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for mores that I've seen before include "Social customs of a group" , "Customs, manners" , "Conventional values" , "Fundamental values of a group" , "of St Thomas's" .)

I've seen this clue in The Times.

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