Decide to finish (8)
I believe the answer is:
conclude
I believe this is a double definition.
'decide' is the first definition.
(I've seen this before)
'to finish' is the second definition.
(concluding is a kind of finishing)
(Other definitions for conclude that I've seen before include "Finally decide" , "Bring or come to an end (8)" , "Bring to a close" , "Close, end" , "reach verdict?" .)