Maiden said to be ethical (5)
I believe the answer is:
moral
'be ethical' is the definition.
(synonyms)
'maiden said' is the wordplay.
'maiden' becomes 'm' (cricket abbreviation).
'said' becomes 'oral' (both can mean spoken).
'm'+'oral'='MORAL'
'to' acts as a link.
(Other definitions for moral that I've seen before include "Upright; message of fable" , "Underlying significance of a story or event" , "Lesson that can be drawn from a story" , "Righteous" , "knowing right from wrong" .)