On reflection, singular omelette is somewhat decent (5)
I believe the answer is:
moral
'decent' is the definition.
(thesaurus)
'on reflection singular omelette is somewhat' is the wordplay.
'on reflection' says the letters should be written in reverse.
'is somewhat' says the answer is hidden in the clue.
'larom' is hidden in the letters of 'singular omelette'.
'larom' written backwards gives 'MORAL'.
(Other definitions for moral that I've seen before include "Lesson of a fable" , "Virtuous and principled" , "Lesson that can be drawn from a story" , "Righteous" , "Pertaining to right and wrong conduct" .)