Prat in army is most grating (8)

I believe the answer is:

hoarsest

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

'prat in army' is the wordplay.
'prat' becomes 'arse' (synonyms).
'in' is an insertion indicator.
'army' becomes 'host' (host is a kind of army).
'arse' inserted into 'host' is 'HOARSEST'.

'is' acts as a link.

Can you help me to learn more?

(Another definition for hoarsest that I've seen is " most husky voice".)

I've seen this clue in The Independent.

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