Be at one match (5)
I believe the answer is:
agree
This clue is a double definition.
'be at one' is the first definition.
(to be of one mind on something)
'match' is the second definition.
(as in two tallies agreeing or matching)
(Other definitions for agree that I've seen before include "'Birds in their little nest . . . . .'" , "Hold the same view" , "Arrive at a settlement" , "Enjoy view in common" , "Square" .)