函 hán correspondence

源How it came to be

An arrow drawn point-down inside a quiver, the case closed round it. It was the case first; what came to be sent in a case was a letter, and the word went with it.

用How it is used

• A formal letter/correspondence - 来函 (láihán) an incoming letter, 公函 (gōnghán) an official letter, 函授 (hánshòu) correspondence course.
• More formal than 信 (xìn); used for official and business correspondence.
• Separately, the math term 函数 (hánshù) function - an unrelated technical use.

字Characters built with 函

• 涵 to wet