noun
letter received; incoming letter
Refers to a letter that has been received, often used in formal or written contexts. Not a common everyday word; 手紙 (てがみ) is the general term for 'letter'.
先日、ご来信をいただきありがとうございます。
Thank you for the letter I received the other day.
来信の内容について検討いたします。
We will consider the contents of your letter.