Hirsute, topless, nonchalant (4)
I believe the answer is:
airy
'nonchalant' is the definition.
(airy can mean casual or unconcerned)
'hirsute topless' is the wordplay.
'hirsute' becomes 'hairy' (synonyms).
'topless' means to remove the first letter.
'hairy' with its first letter removed is 'AIRY'.
(Other definitions for airy that I've seen before include "Old astronomer" , "Fanciful" , "Lacking substance" , "Spacious - aerial" , "Delicate; well ventilated" .)