tube

1. Origins, structure, and basic meaning

• Structure: 筒 has 12 strokes and denotes a hollow tubular shape.
• Basic usage: 筒 is read つつ, and 封筒 is read ふうとう.

2. Common pitfalls and similar expressions

• A tube and an envelope
  • 筒の形 means a tubular shape.
  • 細長い筒に入れた means putting something in a long, narrow tube.
  • 白い封筒に入れて describes putting something in a white envelope.
  • 封筒 names an envelope for letters and similar contents.