Learner's definition of STAIR
1 stairs [plural] : a series of steps that go from one level or floor to another
She ran down the stairs.
He waited at the foot/bottom of the stairs.
She slipped and fell down the stairs.
The stairs lead to the roof.
We had to climb another flight/set of stairs to get to the roof.
2 [count] : one of the steps in a set of stairs