Be of one mind (5)
I believe the answer is:
agree
'be of one mind' is the definition.
(two people who are of one mind are in agreement)
This is the entire clue.
(Other definitions for agree that I've seen before include "Arrive at a settlement" , "Think alike" , "'Assent, concur (5)'" , "Shake on it" , "Go well together" .)