Partner not finishing everything (3)
I believe the answer is:
all
'everything' is the definition.
(I've seen this before)
'partner not finishing' is the wordplay.
'partner' becomes 'ally' (I've seen this in other clues).
'not finishing' means to remove the last letter.
'ally' with its final letter taken off is 'ALL'.
(Other definitions for all that I've seen before include "The works" , "Everything or everyone" , "None excluded" , "Everyone - complete" , "The whole quantity" .)