Set of steps (6)
'set of steps' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ladder that I've seen before include "Climbing structure" , "Row of unravelled stitches" , "Set of steps" , "Run in stockings" , "See 12" .)
(Other definitions for stairway that I've seen before include "A flight of fixed indoor steps" , "- to Heaven, Led Zeppelin song" .)