stair·step 
(stârstĕp′)
(stârstĕp′)n.
1. A step in a staircase.
2. stairsteps A staircase.
3. One of a series of objects or items grouped progressively according to height.
tr. & intr.v. stair·stepped, stair·step·ping, stair·steps
To position or be positioned progressively according to height: images stairstepped on a computer screen; ledges stairstepping down a mountainside.