stair

noun
  1. A step or one of a series of steps for going from one level to another, typically inside a building. noun
    She tripped on the last stair and almost fell.
    The old house had a creaky wooden stair leading to the attic.
  2. A series or flight of steps; a staircase. noun
    He ascended the stairs quickly to catch the train.
    The grand staircase in the mansion was made of marble.