内側

1. Origins, structure, and basic meaning

• Structure: The spelling is 内側, read うちがわ, and it combines 内, meaning inside, with 側, meaning side or surface.
• Basic usage: 内側 is the inside or inner surface of a box, garment, boundary, or other object, opposed to its outside.

2. Common pitfalls and similar expressions

• The interior of a container and the inward-facing side of clothing
  • Both examples use the form 内側. It identifies the surface inside a box or the side of a jacket facing the body.
• A name inside a box and a warmer inside a jacket
  • 箱の内側に名前を書いた。 — I wrote my name inside the box.
  • 寒いので上着の内側に使い捨てカイロを貼った。 — Because it was cold, I attached a disposable warmer to the inside of my jacket.