Why is the ninth month called September?
c.1200, "graphic symbol, alphabetic sign, written character," from Old French letre (10c., Modern French lettre) "character, letter; missive, note," in plural, "literature, writing, learning," from Latin littera (also litera) "letter of the alphabet," of uncertain origin, perhaps via Etruscan from Greek diphthera "tablet," with change of d- to l- as in lachrymose. In this sense it replaced Old English bocstæf, literally "book staff" (cf. 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," a sense first attested in English early 13c., replacing Old English ærendgewrit, literally "errand-writing." The Latin plural also meant "literature, books," and figuratively "learning, liberal education, schooling" (see letters). School letter in sports, attested by 1908, were said to have been first awarded by University of Chicago football coach Amos Alonzo Stagg. Expression to the letter "precisely" is from 1520s (earlier as after the letter). Letter-perfect is from 1845, originally in theater jargon, in reference to an actor knowing the lines exactly. Letter-press, in reference to matter printed from relief surfaces, is from 1840.
"one who lets" in any sense, c.1400, agent noun from let (v.).
in Rom. 2:27, 29 means the outward form. The "oldness of the letter" (7:6) is a phrase which denotes the old way of literal outward obedience to the law as a system of mere external rules of conduct. In 2 Cor. 3:6, "the letter" means the Mosaic law as a written law. (See WRITING.)