Outside dilapidated flat (7)
I believe the answer is:
tedious
'flat' is the definition.
(thesaurus)
'outside dilapidated' is the wordplay.
'dilapidated' indicates anagramming the letters.
'outside' with letters rearranged gives 'TEDIOUS'.
(Other definitions for tedious that I've seen before include "Long, slow, dull" , "Tiresome, boring" , "Outside (anag.)" , "awfully boring" , "not worth listening to?" .)