Record some regret, nervously rejected (5)
I believe the answer is:
enter
'record' is the definition.
('enter' can be a synonym of 'record')
'some regret nervously rejected' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'rejected' says the letters should be written backwards.
'retne' is hidden in the letters of 'regret nervously'.
'retne' backwards is 'ENTER'.
(Other definitions for enter that I've seen before include "Take part in a contest" , "Come or go in" , "put in for a race" , "Fill in" , "Move into" .)