Indicate agreement (3)
I believe the answer is:
nod
'indicate agreement' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nod that I've seen before include "positive sign" , "Signify consent" , "OT land" , "'A . . . is as good as a wink to a blind horse'" , "Asleep in the land" .)