1. letteral - Noun
2. letteral - Adjective
(historical) Referring to a type of musical notation used by Shakers, based on letters instead of notes.
(rare) Regarding letters of the alphabet.
(printing) Obsolete form of literal (“a misprint that affects a letter”).
(Lojban) The name of a letter, such as gy. for the letter G.
Source: en.wiktionary.org