first floor vs storey

first floor and storey both are nouns.

Word	Noun	Adjective	Verb	Adverb
first floor	Yes	No	No	No
storey	Yes	No	No	No

As nouns, storey is a hypernym of first floor; that is, storey is a word with a broader meaning than first floor:

first floor: the floor of a building that is at or nearest to the level of the ground around the building
storey: a structure consisting of a room or set of rooms at a single position along a vertical scale

Other hypernyms of first floor include floor, level, story.

first floor (noun)	storey (noun)
the floor of a building that is at or nearest to the level of the ground around the building	a structure consisting of a room or set of rooms at a single position along a vertical scale