階（かい、kai）
- floor

The Japanese word 階階 (かい) primarily means "floor" or "story" of a building. It indicates the level of a building. It can also refer to "grade" or "rank" in some contexts, such as within a social hierarchy, but the primary meaning relates to buildings. The word itself suggests a level or a step.

⚫︎二階 Translation: Second floor. ⚫︎三階建てのビル Translation: A three-story building.

You use 階階 when specifying the floor of a building. It follows a number, such as 一 (ichi - one), 二 (ni - two), 三 (san - three) to indicate which floor is referenced. It is also used to count floors in a building, using counters. For instance, you might use it when describing where someone lives, or in directions.

The word is typically written as 階階 using the kanji. The reading is かい in hiragana. There are no other common ways to write this word. The okurigana is fixed and the use of hiragana is 階階.

There aren't many direct synonyms for "floor" in the same way, but other words could be used depending on context: ⚫︎ フロア (furoa) - This is a loanword from English, meaning floor. ⚫︎ レベル (reberu) - This is a loanword from English, meaning level, sometimes used to refer to a floor.

There isn't a direct antonym for 階階, as it’s a positional descriptor. However, you could consider the absence of a floor, or the ground level, which might be represented by: ⚫︎ 地下 (chika) - Underground/Basement. ⚫︎ 地上 (chijou) - Above ground/on the surface.

このデパートは五階にあります。 ・Translation: This department store is on the fifth floor. ・Explanation: This sentence uses 階階 (kai) to specify the location of the department store within the building.

彼女はマンションの十階に住んでいます。 ・Translation: She lives on the tenth floor of an apartment building. ・Explanation: This uses 階階 (kai) to indicate the floor of the apartment where the person lives.

The kanji 階階 is composed of the components 阝(left side; associated with the left side of the house) and 皆(right side; meaning "all" or "everyone"). The combination suggests the idea of a level accessible to all, or a level that everyone can access, which makes sense within the context of a building's floors.