Lustful desire (6)
I believe the answer is:
libido
'lustful desire' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for libido that I've seen before include "Emotional energy associated with sexual desire" , "Emotional craving" , "I'd boil over with sexual energy" , "Sexual drive" , "Strong urge" .)