Supermarket's style (4)

I believe the answer is:

perm

I'm a little stuck... Click here to teach me more about this clue!

'style' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'supermarket's' is the wordplay.
'PERM' is hidden in amongst the letters.
But, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for perm that I've seen before include "Wavy hairstyle" , "locks far from straight?" , "A hairdo; Urals city" , "Hair style (abbr)" , "Old-fashioned haircut" .)

I've seen this clue in The Mirror.

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