Special soldiers sautéed at front for US brass (4)

I believe the answer is:

sass

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'us brass' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'special soldiers sauteed at front' is the wordplay.
'special soldiers' becomes 'SAS' (Special Air Service in UK army).
'at front' indicates taking the first letters.
The first letter of 'sauteed' is 's'.
'sas'+'s'='SASS'

'for' is the link.

Can you help me to learn more?

(Another definition for sass that I've seen is " Cheek".)

I've seen this clue in The Times and The Sunday Times.

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