ladder vs stairs

ladder and stairs both are nouns.

Word	Noun	Adjective	Verb	Adverb
ladder	Yes	No	Yes	No
stairs	Yes	No	No	No

As nouns, stairs is a hypernym of ladder; that is, stairs is a word with a broader meaning than ladder:

ladder: steps consisting of two parallel members connected by rungs; for climbing up or down
stairs: a flight of stairs or a flight of steps

Other hypernyms of ladder include steps.

ladder (noun)	stairs (noun)
steps consisting of two parallel members connected by rungs; for climbing up or down	a flight of stairs or a flight of steps
a row of unravelled stitches
ascending stages by which somebody or something can progress

ladder (verb)	stairs (verb)
come unraveled or undone as if by snagging