1 character, symbol, sign:
Epsilon is a letter in the Greek alphabet.
2 missive, epistle, communication, note, line, message, dispatch or despatch; correspondence:
Write me a letter when you get there.
3 letters. literature, the humanities, belles-lettres, the classics; erudition, culture, the world of letters, learning, scholarship:
He is a widely known man of letters.
4 to the letter. precisely, literally, exactly, accurately, strictly, sic, thus, letter for letter, literatim, word for word, verbatim:
The document has been copied to the letter.
5 inscribe, write, spell (out):
She carefully lettered the caption under the picture.