staircase parts (5)
I believe the answer is:
steps
'staircase parts' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for steps that I've seen before include "Stairs; paces" , "Buchan's 1915 novel has 39 of them" , "Footfalls" , "taken to get on" , "Sequence of foot movements in a dance" .)