room

1. Origins, structure, and basic meaning

• Structure: 室 conveys a room or indoor space; its on-reading is しつ.
• Basic usage: 教室（きょうしつ） means a classroom or a class, while 室内（しつない） means indoors or the interior.

2. Common pitfalls and similar expressions

• A classroom as a place and a class as an activity
  • The 教室 whose windows are opened is a room used for lessons. 料理教室 means a cooking class, so 教室 does not always refer only to a physical room.
  • 室内 refers to the inside of a building rather than specifically to a teaching space. 室内で means indoors, and 室内の明るさ means the brightness indoors.