Definition of letter:
a written message addressed to a person or organization; "mailed an indignant letter to the editor"
the conventional characters of the alphabet used to represent speech; "his grandmother taught him his letters"
owner who lets another person use something (housing usually) for hire
a strictly literal interpretation (as distinct from the intention); "he followed instructions to the letter"; "he obeyed the letter of the law"
an award earned by participation in a school sport; "he won letters in three sports"
win an athletic letter
set down or print with letters
mark letters on or mark with letters