Couple's net worth? Not entirely (3)
I believe the answer is:
two
'couple's' is the definition.
(thesaurus)
'net worth? not entirely' is the wordplay.
'not entirely' says the answer is hidden in the clue.
'TWO' can be found hidden inside 'net worth'.
(Other definitions for two that I've seen before include "Number of Gentlemen of Verona" , "Company allegedly" , "Number in company, some say" , "Minimal number of partners" , "II" .)