trembles (6)
I believe the answer is:
shakes
'trembles' is the definition.
('shake' can be a synonym of 'tremble')
This is the entire clue.
(Other definitions for shakes that I've seen before include "jars" , "Frothy drink of milk and flavouring" , "Quivers" , "Judders" , "Moves quickly up and down, say milk drink" .)