Windy apartment building, unlet (9)
I believe the answer is:
flatulent
'windy' is the definition.
(thesaurus)
'apartment building unlet' is the wordplay.
'apartment' becomes 'flat' (synonyms).
'building' indicates anagramming the letters.
'unlet' is an anagram of 'ulent'.
'flat'+'ulent'='FLATULENT'
(Other definitions for flatulent that I've seen before include "Suffering from wind or gas" , "Suffering from excessive intestinal gas" .)