> The actual original meaning of “literal”: “of or pertaining to letters of the alphabet; of the nature of letters, alphabetical” is attested since 1475.

That meaning comes from the Latin "littera"/"litera", meaning letter or character. Words like "transliteration" are based on this root meaning (https://www.etymonline.com/word/transliteration)

Here's the page for "literal": https://www.etymonline.com/word/literal