Positive motion (3)
I believe the answer is:
nod
'positive motion' 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 "Gesture of acceptance" , "Be agreeably" , "OT land" , "Signify agreement" , "It's said to be as good as a wink" .)