das Geschoss
floor
A floor or story in a building.
Wir wohnen im dritten Geschoss des neuen Wohnblocks.
We live on the third floor of the new apartment block.

floor / projectile
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floor
A floor or story in a building.
Wir wohnen im dritten Geschoss des neuen Wohnblocks.
We live on the third floor of the new apartment block.

The word 'Geschoss' (projectile / floor) is derived from the verb 'schießen' (to shoot). A 'Geschoss' is therefore literally something that is 'geschossen' (shot). This origin directly explains the meaning as a projectile and historically also the meaning as a floor or story (the height that people used to be able to build or, figuratively, 'shoot upward').
Der Jäger lud ein neues Geschoss in sein Gewehr.
The hunter loaded a new projectile into his rifle.
The two meanings can be easily distinguished by context. If people are talking about buildings, apartments, or addresses, a floor is meant. If it is about weapons, the military, or crime, a projectile is meant.
Das Büro befindet sich im obersten Geschoss.
The office is located on the top floor.
In connection with floors, there are fixed terms: the lowest floor is the 'Erdgeschoss' (ground floor), the floors above it are 'Obergeschosse' (upper floors), and the floor directly under the roof is the 'Dachgeschoss' (attic floor / top floor).
Die Wohnung im Erdgeschoss hat einen eigenen Garten.
The apartment on the ground floor has its own garden.
To indicate a location, you use 'im Geschoss' (on/in the floor; dative). To express movement to that place, you use 'ins Geschoss' (to/into the floor; accusative).
Der Aufzug fährt bis ins zehnte Geschoss.
The elevator goes up to the tenth floor.
plain / level
'Ebene' and 'Geschoss' can both refer to a level in a building. 'Geschoss' is especially common in construction plans, listings, or official texts. 'Ebene' sounds more general and fits well when a building is organized by levels, for example a parking garage or a large center. In normal conversation, people often say 'Stockwerk' or 'Etage' instead. There is a risk of confusion because 'Geschoss' can also mean something completely different, namely a fired projectile; here, however, it is only about the meaning in a building.

Das neue Büro liegt im obersten Geschoss des Gebäudes.
The new office is on the top floor of the building.
Wegen der Baustelle ist Ebene 1 im Parkhaus heute geschlossen.
Because of the construction work, Level 1 in the parking garage is closed today.