BOHGUN RENOVATIONS Stair is the term that appears in compounds having to do with architectural structures: staircase, stairway, stairwell. Meanwhile step lends itself to figurative use, as in "every step of the process." And that may not be all there is to say about steps and stairs, but it's a step in the right direction.

Treads are the actual steps, where you put your foot as you climb the stairs.