Scenery firm in Derby's not near (5)
I believe the answer is:
decor
'scenery' is the definition.
(thesaurus)
'firm in derby's not near' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'in' is an insertion indicator.
'not' is a deletion indicator.
'near' becomes 'by' (I've seen this in other clues).
'derby' with 'by' taken away is 'der'.
'co' placed within 'der' is 'DECOR'.
(Other definitions for decor that I've seen before include "Style of furnishings, drapes etc used in a room" , "Interior layout and furnishings" , "Furnishings and colours of a room" , "Colour scheme, furnishing etc. of a room" , "stage background" .)