1. A written communication that is usu. enclosed in an envelope, sealed, stamped, and delivered (esp., an official written communication) (an opinion letter).
2. (usu. pl.) A written instrument containing or affirming a grant of some power or right (letters testamentary). [Cases: Executors and Administrators 27. C.J.S. Executors and Administrators ¡ì 79.]
3. Strict or literal meaning (the letter of the law). ? This sense is based on the sense of a letter of the alphabet. Cf. SPIRIT OF THE LAW.