a set of steps built for going from one level of a building to another [↪ upstairs, downstairs]
up/down the stairs
Jerry ran up the stairs.
the top/head of the stairs
I left my briefcase at the top of the stairs.
the bottom/foot of the stairs
'Lisa,' he cried from the foot of the stairs.
We walked up four flights of stairs (=sets of stairs).
one of the steps in a set of stairs:
Lucy sat down on the bottom stair.
3 [singular] literaryDHHTBB
4 British English old-fashioned
in the servants' part of a large house, in the past