Moralist's wordy joke about a girl (7)

I believe the answer is:

puritan

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'moralist's' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for puritan that I've seen before include "One forgoing pleasure" , "Moralistic type" , "Dour Protestant" , "Person of extreme moral strictness" , "Strict person for whom pleasure is sinful" .)

I've seen this clue in the Evening Standard.

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