天井

1. Origins, structure, and basic meaning

• Structure: 天井 is read as てんじょう and is an architectural noun for the upper interior surface of a room, marked with に as the location of a fixture or stain.
• Basic usage: It is used for a light attached overhead or a leak stain appearing on the inside surface.

2. Common pitfalls and similar expressions

• Location particle
  • Both an attached light and an appearing stain use 天井に to mark the location.
• Not the roof
  • It is the interior ceiling, distinct from 屋根, the exterior roof of a building.