Act it badly in the loft (5)
I believe the answer is:
attic
'the loft' is the definition.
(synonyms)
'act it badly' is the wordplay.
'badly' is an anagram indicator.
'act'+'it'='actit'
'actit' is an anagram of 'ATTIC'.
'in' is the link.
(Other definitions for attic that I've seen before include "Floor" , "Classically elegant" , "Top storey" , "Ancient Greek; loft" , "High level of" .)