Carefree coitus with Nina Cook (10)
I believe the answer is:
insouciant
'carefree' is the definition.
(I've seen this in another clue)
'coitus with nina cook' is the wordplay.
'with' means one lot of letters go next to another.
'cook' indicates an anagram.
'coitus' after 'nina' is 'ninacoitus'.
'ninacoitus' anagrammed gives 'INSOUCIANT'.
(Other definitions for insouciant that I've seen before include "Laid-back" , "Carefree, heedless" , "Untroubled" , "Not concerned" , "Light-hearted - in auctions (anag)" .)