Prop on an empty stairway (4)
I believe the answer is:
stay
'prop' is the definition.
(I've seen this in another clue)
'an empty stairway' is the wordplay.
'an empty' says to hollow out the word (remove centre letters).
'stairway' with its middle taken out is 'STAY'.
'on' acts as a link.
(Other definitions for stay that I've seen before include "Stick around" , "Period in one place" , "Remain; detain" , "Remain; guy" , "control" .)