Most remorseful about shock (6)
I believe the answer is:
tremor
'shock' is the definition.
(I have seen 'Small shock ' mean 'tremor' so perhaps 'shock' could also mean 'tremor')
'most remorseful about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'TREMOR' is hidden within 'most remorseful'.
(Other definitions for tremor that I've seen before include "Quavering" , "Minor earthquake" , "Minor quake" , "A slight shake, body or earth" , "Involuntary shudder" .)