Webster's Revised Unabridged Dictionary · 1913

Stair

Stair (stâr) , noun

[Old English steir, steyer, Anglo-Saxon stager, from stīgan to ascend, rise. r164. See Sty to ascend.]

1.
One step of a series for ascending or descending to a different level; -- commonly applied to those within a building.
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.
I a winding stair found. — Chaucer's Dream
Collocations (6)
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 (Architecture) , 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.