ground floor vs storey

ground floor and storey both are nouns.

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

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

ground 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 ground floor include floor, level, story.

ground 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
becoming part of a venture at the beginning (regarded as position of advantage)