Joke about Rita having strict morals (7)

I believe the answer is:

puritan

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'strict morals' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

'joke about rita' is the wordplay.
'joke' becomes 'pun' (pun is a type of joke).
'about' is an insertion indicator.
'pun' going around 'rita' is 'PURITAN'.

'having' is the link.

Can you help me to learn more?

(Other definitions for puritan that I've seen before include "Calvinist Protestant" , "Prude" , "Strictly moral person" , "narrow-minded" , "Killjoy" .)

I've seen this clue in The Sun.

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