stairs stairs /ˈstɛrz/

noun

1. () A flight of stairs or a flight of steps  ( stairs , steps )
   a flight of stairs or a flight of steps
     She climbed the stairs to the second floor.
   She climbed the stairs to the second floor.
   
   

 stair stair /ˈstɛr/

noun

1. () Support consisting of a place to rest the foot while ascending or descending a stairway  ( stair , step )
   support consisting of a place to rest the foot while ascending or descending a stairway
    He paused on the bottom step
   he paused on the bottom step