Rascally, good-hearted libertine (5)
I believe the answer is:
rogue
'rascally good-hearted libertine' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'good-hearted libertine' is the wordplay.
'good' becomes 'g' (abbreviation).
'hearted' is an insertion indicator (some letters go to the heart of the word).
'libertine' becomes 'roue' (roue is a kind of libertine).
'g' put within 'roue' is 'ROGUE'.
Can you help me to learn more?
(Other definitions for rogue that I've seen before include "A dishonest or unprincipled person" , "Villain - freak" , "Miscreant" , "Old Greek" , "Bad guy" .)