A number of elms (4)

I believe the answer is:

nine

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This clue could be a double definition.

'a number' is the first definition.
(nine is a number)

'of elms' is the second definition.
The definition suggests a singular noun which matches the answer.

Can you help me to learn more?

(Other definitions for nine that I've seen before include "One's married partner" , "One more than fourteen across" , "SECOND PART OF 14" , "3x3" , "Square number" .)

I've seen this clue in the Evening Standard.

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