The noun letter has 5 senses (first 4 from tagged texts)
1. (475) letter, missive -- (a written message addressed to a person or organization; "mailed an indignant letter to the editor")
2. (51) letter, letter of the alphabet, alphabetic character -- (the conventional characters of the alphabet used to represent speech; "his grandmother taught him his letters")
3. (2) letter -- (a strictly literal interpretation (as distinct from the intention); "he followed instructions to the letter"; "he obeyed the letter of the law")
4. (1) letter, varsity letter -- (an award earned by participation in a school sport; "he won letters in three sports")
5. letter -- (owner who lets another person use something (housing usually) for hire)
Overview of verb letter
The verb letter has 3 senses (first 1 from tagged texts)
1. (1) letter -- (win an athletic letter)
2. letter -- (set down or print with letters)
3. letter -- (mark letters on or mark with letters)