Door opens, holding cord (4)
I believe the answer is:
rope
'cord' is the definition.
(rope is a kind of cord)
'door opens holding' is the wordplay.
'holding' says the answer is hidden in the clue.
'ROPE' can be found hidden inside 'door opens'.
(Other definitions for rope that I've seen before include "'Cable, cord (4)'" , "Lasso?" , "Give a man enough . . . . and he'll hang himself" , "Lash" , "Master of Suspense directed it" .)