A middling meal? (5)

I believe the answer is:

lunch

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

This clue might be a double definition.

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

'meal' is the second definition.
(lunch is a kind of meal)

Can you help me to learn more?

(Another definition for lunch that I've seen is " Midday meal".)

I've seen this clue in the Evening Standard.

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