Cold-blooded fish occupying dirty home (6)
I believe the answer is:
steely
'cold-blooded' is the definition.
(thesaurus)
'fish occupying dirty home' is the wordplay.
'fish' becomes 'eel' (eel is a kind of fish).
'occupying' indicates putting letters inside.
'dirty home' becomes 'sty' (as in a pig sty).
'eel' inserted inside 'sty' is 'STEELY'.
(Other definitions for steely that I've seen before include "With (cold) resolve" , "Gimlet-eyed" , "Coldly determined" , "Hard and metallic" , "Set off" .)