封

1. Origins, structure, and basic meaning

• Structure: 封(ふう) denotes the sealed state of an envelope or similar object, or its sealed closure.
• Basic usage: It describes an old photograph emerging when an envelope's seal is broken.
  • 手紙の封を切ると、中から古い写真が出てきた。

2. Common pitfalls and similar expressions

• Sealing and opening
  • 封をする means sealing something, while 封を切る means breaking the seal to open it. 封筒(ふうとう) instead denotes the envelope itself.