Revealed about protein source (4)

I believe the answer is:

veal

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'protein source' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.

'revealed about' is the wordplay.
'about' indicates a hidden word (the clue goes around or about the answer).
'VEAL' is hidden within 'revealed'.

Can you help me to learn more?

(Other definitions for veal that I've seen before include "Calves' flesh as food" , "Calf flesh" , "Calf's flesh as food" , "Type of meat" , "White meat" .)

I've seen this clue in The Mirror.

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