Listless cheat with girl confused (9)
I believe the answer is:
lethargic
'listless' is the definition.
(similar in meaning)
'cheat with girl confused' is the wordplay.
'with' means one lot of letters go next to another.
'confused' indicates an anagram.
'cheat' put after 'girl' is 'girlcheat'.
'girlcheat' anagrammed gives 'LETHARGIC'.
(Other definitions for lethargic that I've seen before include "languid" , "Unenergetic" , "Short of energy" , "somewhat slow" , "reluctant to move" .)