your letter; correspondence from you
Polite noun used in formal writing to refer to a letter or communication received from the addressee. Often seen in business or official contexts.
I have received your letter.
Regarding the matter you requested in your recent correspondence, I have taken note.
Compound of 貴 (ki, 'honorable, your') and 信 (shin, 'letter, message'). The prefix 貴 is commonly used in polite language to refer to things belonging to the addressee.