Number, a score (6)
I believe the answer is:
twenty
I believe this clue is a double definition.
'number' is the first definition.
(twenty is a kind of whole number)
'a score' is the second definition.
(I've seen this before)
(Other definitions for twenty that I've seen before include "Figure" , "Number" , "previous clue?" , "made by Q on a light blue square" , "Hundredweights to a ton" .)