Flat meant part was wrong (9)
I believe the answer is:
apartment
'flat' is the definition.
(I know that flat can be written as apartment)
'meant part was wrong' is the wordplay.
'was wrong' indicates an anagram (I've seen 'is wrong' mean this).
'meant'+'part'='meantpart'
'meantpart' is an anagram of 'APARTMENT'.
(Other definitions for apartment that I've seen before include "Penthouse" , "Flat (chiefly US)" , "pad" , "quarters" , "Room ? flat" .)