Associate failing to finish everything (3)
I believe the answer is:
all
'everything' is the definition.
(all things)
'associate failing to finish' is the wordplay.
'associate' becomes 'ally' (ally is a kind of associate).
'failing to finish' means to remove the last letter.
'ally' with its last letter taken off is 'ALL'.
(Other definitions for all that I've seen before include "Completely, everything" , "100%" , "without exception" , "that's as many as there are" , "Quite" .)