Silently agrees (4)
I believe the answer is:
nods
'silently agrees' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nods that I've seen before include "Affirmative gestures" , "Signals assent" , "gestures in agreement" , "Non-verbal indications of assent" , "Makes mistake" .)