Notice partial twitch (3)
I believe the answer is:
tic
'twitch' is the definition.
(I know that tic is a type of twitch)
'notice partial' is the wordplay.
'partial' indicates a hidden word.
'TIC' is hidden in the letters of 'notice'.
(Other definitions for tic that I've seen before include "jerk" , "Nervous movement" , "Localised habitual twitch, especially to the face" , "Regular muscular twitch" , "Jerky movement" .)