Shake with most remorse (6)
I believe the answer is:
tremor
'shake' is the definition.
(I know that tremor is a more specific form of shake)
'with most remorse' is the wordplay.
'with' says the answer is hidden in the clue.
'TREMOR' is hidden in the letters of 'most remorse'.
(Other definitions for tremor that I've seen before include "Minor earthquake" , "A slight shake, perhaps of earth" , "Shiver in the earth" , "make one shake" , "Involuntary shudder" .)