Lived initially in large apartment (4)
I believe the answer is:
flat
'apartment' is the definition.
(I know that apartment can be written as flat)
'lived initially in large' is the wordplay.
'initially' says to take the initial letters.
'in' indicates putting letters inside.
'large' becomes 'fat' (I've seen this in other clues).
The first letter of 'lived' is 'l'.
'l' inserted inside 'fat' is 'FLAT'.
(Other definitions for flat that I've seen before include "12 [TWO DIMENSIONAL]" , "Puncture" , "Horizontal" , "Dull; apartment" , "Unnatural - uninteresting - apartment" .)