mezzanine vs storey

mezzanine and storey both are nouns.

Word	Noun	Adjective	Verb	Adverb
mezzanine	Yes	No	No	No
storey	Yes	No	No	No

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

mezzanine: intermediate floor just above the ground floor
storey: a structure consisting of a room or set of rooms at a single position along a vertical scale

Other hypernyms of mezzanine include floor, level, story.

mezzanine (noun)	storey (noun)
intermediate floor just above the ground floor	a structure consisting of a room or set of rooms at a single position along a vertical scale
first or lowest balcony