Food may be returned to school (4)

I believe the answer is:

yams

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'food may be returned to school' is the definition.
I can't judge whether this defines the answer.

'may be returned to school' is the wordplay.
'be returned' says the letters should be written backwards (I've seen 'is returned' mean this).
'to school' becomes 'S'.
'may' reversed gives 'yam'.
'yam'+'s'='YAMS'

Can you help me to learn more?

(Other definitions for yams that I've seen before include "Roots" , "Edible tubers from the tropics" , "vegetables" , "Sweet potatoes" .)

I've seen this clue in The Mirror.

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