Partially decorates a long room (5)
I believe the answer is:
salon
'room' is the definition.
(salon is a kind of room)
'partially decorates a long' is the wordplay.
'partially' indicates a hidden word.
'SALON' is hidden in the letters of 'decorates a long'.
(Other definitions for salon that I've seen before include "Formal sitting room" , "Hairdresser's premises" , "where cuts are commonplace" , "Elegant room is great house for entertaining" , "Drawing-room" .)