Doubles a number and a number (8)
I believe the answer is:
foursome
'doubles' is the definition.
(thesaurus)
'a number and a number' is the wordplay.
'a number' becomes 'four' (four is a kind of number).
'and' is a charade indicator (letters next to each other).
'a number' becomes 'some' (I have seen 'Undefined number ' mean 'some' so perhaps 'number' could also mean 'some').
'four'+'some'='FOURSOME'
(Other definitions for foursome that I've seen before include "The Beatles, for example" , "In game" , "golf match" , "Quartet" , "Tennis doubles players, for example" .)