天井（てんじょう、tenjou）
- ceiling

The word 天井 (てんじょう) primarily refers to the ceiling of a room or building. It is the upper interior surface that covers a room. It can also figuratively refer to the highest limit or the peak of something, although this usage is less common.

⚫︎部屋の天井 Translation: The ceiling of the room ⚫︎天井に電球を取り付ける Translation: To install a lightbulb on the ceiling. ⚫︎株価が天井に達した。 Translation: The stock price reached its peak.

You use 天井 when talking about the upper part of a room or structure. For example, when describing the height of a room, or pointing out a detail on the ceiling, such as a light fixture or a crack. The figurative usage is less common but can be used when discussing a limit or a high point.

天井 is typically written in kanji as 天井, and the reading is てんじょう in hiragana. There are no other common ways to write this word. The okurigana is standard, with no variations.

There are no direct synonyms for the word 天井 in the context of the ceiling. For the figurative meaning of "peak" or "highest limit," you could use words such as: ⚫︎ 頂点(ちょうてん) - peak, summit ⚫︎ 最高点(さいこうてん) - the highest point.

There aren't many direct antonyms because 天井 specifically refers to the ceiling. However, you could consider the "floor" as its opposite: ⚫︎ 床(ゆか) - floor

その部屋の天井はとても高い。 ・Translation: The ceiling of that room is very high. ・Explanation: This sentence describes the height of the ceiling.

天井にカビが生えている。 ・Translation: Mold is growing on the ceiling. ・Explanation: This sentence points out a problem on the ceiling.

The word 天井 is a compound word. 天(てん) means "sky" or "heaven," and 井(せい/しょう) means "well" or "a structure." In this context, it is believed the "井" part refers to the way the beams of a ceiling were structured.