One way to agree (3)
I believe the answer is:
nod
'one way to agree' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nod that I've seen before include "Signify agreement" , "Cain left Eden for the Land of . . ." , "Show recognition" , "Gesture of assent" , "Indicate agreement (or sleepiness!)" .)