A feature of golf — uncompleted match (5)
I believe the answer is:
agree
'match' is the definition.
(agreeing is a kind of matching)
'a feature of golf uncompleted' is the wordplay.
'feature of golf' becomes 'green'.
'uncompleted' means to remove the last letter.
'green' with its last letter taken off is 'gree'.
'a'+'gree'='AGREE'
(Other definitions for agree that I've seen before include "Settle" , "Accept" , "Match; tally" , "get on" , "Consent required" .)