Shake in utmost remorse (6)
I believe the answer is:
tremor
'shake' is the definition.
(I know that tremor is a more specific form of the action shake)
'in utmost remorse' is the wordplay.
'in' indicates a hidden word.
'TREMOR' is hidden in the letters of 'utmost remorse'.
(Other definitions for tremor that I've seen before include "Shudder - quake" , "Quavering" , "A slight shake, perhaps of earth" , "Quivering" , "A small shake, perhaps of earth ( 6)" .)