What part of speech is the word stair?

The word "stair" can be either a noun or an adjective, depending on how it's used in a sentence.

Noun:

* Singular: "I climbed the stair."

* Plural: "The stairs were creaky."

Adjective:

* "The stair railing was made of wrought iron." (Describing the railing)

Let me know if you'd like more examples!