Wordlessly agree (3)
I believe the answer is:
nod
'wordlessly agree' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nod that I've seen before include "Gesture of approval with head" , "Appear to fall asleep" , "What Homer may sometime do" , "Affirmative action?" , "Assenting head gesture" .)