- a pair of letters representing a single speech sound, as ea in meat or th in path.
- a combination of two letters or characters used to represent a single speech sound such as gh in English toughCompare ligature (def. 5), diphthong
1788, in linguistics, from Greek di- “twice” (see di- (1)) + -graph “something written,” from Greek graphe “writing,” from graphein “to write, express by written characters,” earlier “to draw, represent by lines drawn” (see -graphy). In mathematics, from 1955, a contraction of directed graph.