Sudden movement outside old room (6)
I believe the answer is:
lounge
'room' is the definition.
(I know that lounge is a type of room)
'sudden movement outside old' is the wordplay.
'sudden movement' becomes 'lunge' (I've seen this in another clue).
'outside' indicates putting letters inside (some letters go outside others).
'old' becomes 'o' (abbreviation).
'lunge' placed around 'o' is 'LOUNGE'.
(Other definitions for lounge that I've seen before include "Sprawl" , "Room for relaxing" , "Living area" , "Relax in sitting room?" , "Waste time -- glue on (anag)" .)