Birthday boys? (5)

I believe the answer is:

natal

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'birthday' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for natal that I've seen before include "Colony once" , "Like a birthday" , "Of or from one's birth - in S African province" , "dealing with delivery" , "Province of South Africa" .)

I've seen this clue in the Evening Standard.

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