D defs.my
Entry 2 senses Webster, 1913

Stair

/(stâr)/ · IPA /stɛɚ/
01 n. One step of a series for ascending or descending to a different level; -- commonly applied to those within a building.
  1. 1.
    One step of a series for ascending or descending to a different level; -- commonly applied to those within a building.
  2. 2.
    A series of steps, as for passing from one story of a house to another; -- commonly used in the plural; but originally used in the singular only.
Phrases & compounds
Below stairs — in the basement or lower part of a house, where the servants are.
Flight of stairs — the stairs which make the whole ascent of a story.
Pair of stairs — a set or flight of stairs. -- pair, in this phrase, having its old meaning of a set. See Pair, n., 1.
Run of stairs — a single set of stairs, or section of a stairway, from one platform to the next.
Stair rod — a rod, usually of metal, for holding a stair carpet to its place.
Up stairs — See Upstairs in the Vocabulary.