Below par wage? (4,3)

I believe the answer is:

sick pay

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This clue could be a double definition.

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

'wage?' is the second definition.
(I know that sick pay is a type of wage)

Can you help me to learn more?

I've seen this clue in The Guardian.

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