Buddhist scripture seems underwhelming to the atheists, initially (5)

I believe the answer is:

sutta

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'buddhist scripture' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'seems underwhelming to the atheists initially' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'seems underwhelming to the atheists' is 'SUTTA'.

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I've seen this clue in The Independent.

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