Nouns

(n)upstairsthe part of a building above the ground floor“no one was allowed to see the upstairs”

Adjectives

(a)upstairs, upstairon or of upper floors of a building“the upstairs maid”, “an upstairs room”

Adverbs

(r)upstairs, up the stairs, on a higher flooron a floor above“they lived upstairs”
(r)upstairswith respect to the mind“she's a bit weak upstairs”