Eventually commit oneself (4,3,6)
I believe the answer is:
take the plunge
'eventually commit oneself' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for take the plunge that I've seen before include "Finally decide" , "Summon up courage" , "to leave the board" , "Eventually commit oneself" , "Decide on bold action" .)