Letter
Middle English: from Old French lettre, from Latin litera, littera ‘letter of the alphabet’, (plural) ‘epistle, literature, culture’.
wiktionary
From Middle English letter, lettre, from Old French letre, from Latin littera(“letter of the alphabet"; in plural, "epistle”), from Etruscan, from Ancient Greek διφθέρᾱ(diphthérā, “tablet”). Displaced native Middle English bocstaf, bookstave(“letter, alphabetic symbol”) (from Old English bōcstæf(“alphabetic symbol, written character”)), Middle English bocrune, bocroune(“letter, written character”) (from Old English bōc(“book”) + rūn(“letter, rune”)), Middle English writrune, writroune(“letter, document”) (from Old English writ(“letter, epistle”) + rūn(“letter, rune”)), Old English ǣrendbōc(“letter, message”), Old English ǣrendġewrit(“letter, written message”). Doublet of diphtheria.
From Middle English letere, equivalent to let + -er.
etymonline
letter (n.1)
c. 1200, "graphic symbol, alphabetic sign, written character conveying information about sound in speech," from Old French letre "character, letter; missive, note," in plural, "literature, writing, learning" (10c., Modern French lettre), from Latin littera (also litera) "letter of the alphabet," also "an epistle, writing, document; literature, great books; science, learning;" a word of uncertain origin.
According to Watkins, perhaps via Etruscan from Greek diphthera "tablet" (with change of d- to l- as in lachrymose), from a hypothetical root *deph- "to stamp." In this sense it replaced Old English bocstæf, literally "book staff" (compare German Buchstabe "letter, character," from Old High German buohstab, from Proto-Germanic *bok-staba-m).
Latin littera also meant "a writing, document, record," and in plural litteræ "a letter, epistle, missive communication in writing," a sense passed through French and attested in English letter since early 13c. (replacing Old English ærendgewrit "written message," literally "errand-writing"). The Latin plural also meant "literature, books," and figuratively "learning, liberal education, schooling" (see letters).
The custom of giving the school letter as an achievement award in sports, attested by 1908, is said to have originated with University of Chicago football coach Amos Alonzo Stagg. Earlier in reference to colleges it meant "university degree or honor that adds initials to a name" (1888). Expression to the letter "precisely" is from 1520s (earlier after the letter, mid-14c.). Letter-quality (adj.) "suitable for (business) letters" is from 1977. For letters patent (with French word order) see patent (n.).
letter (v.)
"write in letters," 1660s, from letter (n.1). Earlier it was used in a now obsolete sense "instruct" (mid-15c.). Related: Lettered; lettering.
letter (n.2)
"one who lets" in any sense, c. 1400, agent noun from let (v.).
