biliteral

Biliteral is a term used across linguistics and cryptography to denote anything involving two letters or two-letter signs. In general, it can describe a writing mode, symbol, or encoding that relies on two distinct letters, alphabets, or styles. The term is not widely used as a technical label in modern linguistics, where terms such as digraph or two-letter sequence are more common, but it appears in discussions of two-letter sign systems and in historical contexts.

In cryptography, the biliteral cipher is a historic method that encodes plaintext by pairs of symbols drawn from two separate alphabets or typefaces. Each plaintext letter is represented by a two-symbol pair, with the first symbol chosen from one alphabet and the second from the other according to a fixed mapping. This creates a secondary dimension of substitution that can obscure the message within ordinary text when the two alphabets are made to appear similar or when the symbols are concealed in formatting, typography, or layout. Variants may use fonts, ink colors, or spacing to hide the encoding.

In broader usage, biliteral can describe any binary-letter encoding where information is carried by two-letter units rather than single letters. It is related conceptually to digraphs (two-letter combinations that represent a single sound) and to other two-element encoding schemes.

See also: biliteral cipher, digraph, cryptography, writing systems