Most fastidious theologian that is participating in Lent? (8)

I believe the answer is:

faddiest

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'most fastidious' is the definition.
Both the definition and answer are superlative adjectives. Perhaps you can see a link between them that I don't see?

'theologian that is participating in lent?' is the wordplay.
'theologian' becomes 'DD' (Doctor of Divinity degree).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'participating in' means one lot of letters goes inside another.
'lent?' becomes 'fast' (I've seen this before).
'dd'+'ie'='ddie'
'ddie' put within 'fast' is 'FADDIEST'.

Can you help me to learn more?

(Another definition for faddiest that I've seen is " Most finicky".)

I've seen this clue in The Guardian.

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