Fabric spotted outside empty apartment (6)
I believe the answer is:
sateen
'fabric' is the definition.
(I know that sateen is a type of fabric)
'spotted outside empty apartment' is the wordplay.
'spotted' becomes 'seen' (I've seen this before).
'outside' indicates putting letters inside (some letters go outside others).
'empty' says to hollow out the word (remove centre letters).
'apartment' becomes 'apt' (abbreviation in property ads for example).
'apt' with its centre removed is 'at'.
'seen' enclosing 'at' is 'SATEEN'.
(Other definitions for sateen that I've seen before include "Sea net could provide a glossy fabric" , "Shiny cloth found in senate" , "Glossy material" , "Glossy cotton fabric" , "Shiny cloth used for furnishings" .)