Stair part (5)
'stair part' is the definition.
(I know that riser part of stair)
This is the entire clue.
(Other definitions for riser that I've seen before include "Vertical piece between stair steps" , "Front of a step; vertical pipe" , "upright portion of step" , "Vertical part of a stair or step" , "Vertical piece between two stair treads" .)
'stair part' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for step that I've seen before include "Ladder rung; pace" , "Manner of walking" , "Movement in dancing" , "Pace; foothold" , "Part of a stairway" .)