1780 T. Sheridan Gen. Dict. Eng. Lang. App. 63 All improper diphthongs, or, as I have called them, digraphs,..are changed..into the single vowels which they stand for.

1812 J. C. Hobhouse Journey App. 1061 If these combinations of vowels had been distinguished in writing only..their name would have been digraphs, and not dipthongs.

1873 J. Earle Philol. Eng. Tongue (ed. 2) ii. 186 He would therefore recognise the consonantal digraphs ch, gh..sh, th, wh, ng, as alphabetic characters.

1877 H. Sweet Handbk. Phonetics 174 If..we exclude new letters..we are obliged to fall back on digraphs.

1955 F. Harary in Trans. Amer. Math. Soc. 77 445 Our object is..to count various kinds of generalizations of graphs. These include directed graphs (digraphs), rooted graphs [etc.].

1965 F. Harary et al. Structural Models i. 2 The theory of directed graphs, or more briefly ‘digraphs’ (a term suggested by G. Pólya).

1973 C. W. Gear Introd. Computer Sci. vii. 299 A road map in which every road is one-way would be a digraph.

1976 Bondy & Murty Graph Theory with Applications x. 171 Every concept that is valid for graphs automatically applies to digraphs too... However, there are many concepts that involve the notion of orientation, and these apply only to digraphs.

1980 Sci. Amer. Mar. 18/2 No matter how the arrowheads are placed on a complete digraph, there will always be a directed path that visits each point just once. Such a path is called a Hamiltonian.