階段（かいだん、kaidan）
- stairs

The Japanese word 階段 means "stairs" or "staircase." It refers to a series of steps used to go from one level to another in a building or other structure. This can include indoor and outdoor stairways.

⚫︎その 階段 を上（のぼ）ってください。 Translation: Please go up those stairs. ⚫︎新しいマンションにはエレベーターと 階段 があります。 Translation: The new apartment building has an elevator and stairs. ⚫︎急（きゅう）な 階段 をゆっくりと下（くだ）りました。 Translation: I slowly went down the steep stairs.

You use 階段 in any situation where you're referring to stairs. It can be used in everyday conversation, in formal settings, and in written Japanese. Use it when describing the location of stairs, giving directions involving stairs, or discussing the use of stairs.

⚫︎The word is primarily written using kanji and hiragana: 階段. ⚫︎The kanji is 階 (kai), meaning "stair, floor" and 段 (dan), meaning "step, grade." ⚫︎It is always written in hiragana as かいだん. ⚫︎There are no variations in the okurigana (the suffix hiragana) in this case.

⚫︎階段室（かいだんしつ） - Stairwell (refers to the enclosed space containing the stairs) ⚫︎There aren't many direct synonyms, as 階段 itself is the most common term.

⚫︎ There is no direct antonym, as there isn't a single word that means "not stairs." Words like "elevator" エレベーター, which serve the opposite function of stairs, can be considered as antonyms in context.

この 階段 は少し古（ふる）いですが、まだ丈夫（じょうぶ）です。 ・Translation: These stairs are a little old, but they are still sturdy. ・Explanation: This sentence describes the condition of the stairs.

火事（かじ）の時（とき）は、 階段 を使（つか）ってください。 ・Translation: In case of a fire, please use the stairs. ・Explanation: This sentence provides instructions for emergency situations.

The word 階段 is formed from the two kanji: 階 (kai) and 段 (dan). 階 originally meant "step" or "tier," and 段 also means "step" or "grade". The combination therefore directly refers to a staircase or flight of steps.