Number of sheep, possibly, but not goats (8)

I believe the answer is:

singular

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'number' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for singular that I've seen before include "Unique, peculiar" , "number" , "Exceptional, one-off" , "Individual; extraordinary" , "As sheep may be, but not cattle or horses" .)

I've seen this clue in The Times.

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