a. A written symbol or character representing a speech sound and being a component of an alphabet.
b. A written symbol or character used in the graphemic representation of a word, such as the h in Thames. See Note at Thames.
2. A written or printed communication directed to a person or organization.
3. A certified document granting rights to its bearer. Often used in the plural.
4. Literal meaning: had to adhere to the letter of the law.
5. letters(used with a sing. verb)
a. Literary culture; belles-lettres.
b. Learning or knowledge, especially of literature.
c. Literature or writing as a profession.
6. Printing
a. A piece of type that prints a single character.
b. A specific style of type.
c. The characters in one style of type.
7. An emblem in the shape of the initial of a school awarded for outstanding performance, especially in varsity athletics.
v.let·tered, let·ter·ing, let·ters
v.tr.
1. To write letters on.
2. To write in letters.
v.intr.
1. To write or form letters.
2. To earn a school letter, as for outstanding athletic achievement: She lettered in three collegiate sports.
Idiom:
to the letter
To the last detail; exactly: followed instructions to the letter.
[Middle English, from Old French lettre, from Latin littera, perhaps from Etruscan, from Greek diphther, hide, leather, writing surface.]
letter·er n.
Synonyms: letter, epistle, missive, note These nouns denote a written communication directed to another: received a letter of complaint; the Epistles of the New Testament; a missive of condolence; a thank-you note.
letter /ltr/ n.1 a symbol of an alphabet: The letter M follows the letter L. 2 a written message, usu. sent by mail: She sent a letter to her mother.3 a formal document ensuring certain conditions: The king gave the ambassador a letter of safe passage for his trip home.4pl. distinction in learning: The professor is a man of letters.5the letter of the law: the exact written requirements of s.t. (as opposed to its intent or purpose): The judge decided the case according to the letter of the law.6to follow to the letter: to obey precisely, with attention to detail: He told me to follow the instructions to the letter. v.1 [T] to draw or write letters on 2 [I] to earn an athletic award: He lettered in three sports in high school.
Thesaurus: letter n. 1 a character, written symbol 2 a note | missive, epistle frml.
l
t
r/ n. 1 a symbol of an alphabet: The letter M follows the letter L. 2 a written message, usu. sent by mail: She sent a letter to her mother. 3 a formal document ensuring certain conditions: The king gave the ambassador a letter of safe passage for his trip home. 4 pl. distinction in learning: The professor is a man of letters. 5 the letter of the law: the exact written requirements of s.t. (as opposed to its intent or purpose): The judge decided the case according to the letter of the law. 6 to follow to the letter: to obey precisely, with attention to detail: He told me to follow the instructions to the letter. 
v. 1 [T] to draw or write letters on 2 [I] to earn an athletic award: He lettered in three sports in high school.
t
r)
, hide, leather, writing surface.]