Junk in window, a steal (5)
I believe the answer is:
waste
'junk' is the definition.
(thesaurus)
'in window a steal' is the wordplay.
'in' indicates a hidden word.
'WASTE' is hidden within 'window a steal'.
(Other definitions for waste that I've seen before include "kill" , "Atrophy" , "Fritter away" , "Spend to no purpose" , "Sweat (anag)" .)