1. a part of a building comprising all the rooms that are on the same level:"a three-storey building"
Word Originlate Middle English: shortening of Latin historia ‘history, story’, a special use in Anglo-Latin, perhaps originally denoting a tier of painted windows or sculptures on the front of a building (representing a historical subject).
Level part of a building that could be used by people
A storey or story, is any level part of a building with a floor that could be used by people. Plurals for the word are storeys (UK) and stories (US). Wikipedia