heaven · sky

1. Origins, structure, and basic meaning

• Structure: 天 means sky or heaven; its on-reading is てん.
• Basic usage: 天気(てんき) means weather, while 天井(てんじょう) means a room's ceiling.

2. Common pitfalls and similar expressions

• Conditions in the sky and an indoor ceiling
  • 天気 refers to weather conditions, such as clear skies or changeable mountain weather. 天井 is the upper surface of a room, where a light can be fitted or a leak can leave a stain.
  • The latter part of 天井 is read じょう. The whole word is てんじょう.