Fittingly, apartment lay empty (5)
I believe the answer is:
aptly
'fittingly' is the definition.
(I've seen this in another clue)
'apartment lay empty' is the wordplay.
'apartment' becomes 'apt' (abbreviation in property ads for example).
'empty' says to hollow out the word (remove centre letters).
'lay' with its middle removed is 'ly'.
'apt'+'ly'='APTLY'
(Other definitions for aptly that I've seen before include "In suitable fashion" , "Suitably" , "In a competent manner" , "In an appropriate way" , "In suitable form" .)