书信 (shūxìn): letter

Measure Word

一封书信 fēng

Tāmen tōngguò shūxìn bǎochí liánxì.

They kept in touch through letters.

Tā bǎocún zhe suǒyǒu yǔ tā wǎnglái de shūxìn.

She kept all the letters she exchanged with him.

Shūxìn wǎnglái zài gǔdài shì zhòngyào de gōutōng fāngshì.

Written correspondence was an important means of communication in ancient times.

register

书信 is a formal or literary term for a letter. In everyday modern speech, 信 or 信件 are more commonly used.

书 shū

信 xìn