Outer coat, perhaps, used by Argus (5)

I believe the answer is:

sugar

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'outer coat' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'used by argus' is the wordplay.
'argus' anagrams to 'SUGAR'.
Though, I am not sure how the anagram is indicated.

'perhaps' acts as a link.

Can you help me to learn more?

(Other definitions for sugar that I've seen before include "Term of affection" , "Argus (anag.)" , "--- Ray Robinson, boxer" , "Sweet white substance" , "White crystalline sweetener" .)

I've seen this clue in the Evening Standard.

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