Somewhat sour attitude initially tainted cult idea (9)

I believe the answer is:

acidulate

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'attitude initially tainted cult idea' is the definition.
I can't tell whether this defines the answer.

'somewhat sour' is the wordplay.
'somewhat' means to remove the last letter (some but not all of the word).
'sour' becomes 'acidulated' (similar in meaning).
'acidulated' with its final letter removed is 'ACIDULATE'.

Can you help me to learn more?

(Another definition for acidulate that I've seen is " Make slightly sour".)

I've seen this clue in The Times.

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