letter · noun C /ˈlet̬.ər/
letter (MESSAGE)
A1 a written message that you send to someone, usually in the mail
Dictionary example:
I got a letter from Francine this morning.
Learner example:
I got your letter yesterday. (Skills for Life (Entry 1); A1; Luganda)
letter (SYMBOL)
A2 a symbol that is used in written language and that represents a sound in that language
Dictionary example:
the letter D
Learner example:
I bought a pair of yellow and blue jeans. . . . And also a green T-shirt with letters on it. (Key English Test; A2; Spanish)