diphthong

plural diphthongs · alternative obsolete dipthong

1. human sciencesA complex vowel sound that begins with the sound of one vowel and ends with the sound of another vowel, in the same syllable.

   In Lang Belta vowels usually appear preceding or following a consonant (see previous examples), and as of now no occurrence of diphthongs or triphthongs has been attested.

   2021 October 5, Gessica Puccini, “Lang Belta: the Belter language from SYFY/Amazon’s The Expanse”, in Lingoblog

   Synonyms: gliding vowel

2. human sciencesA diaphoneme realized as a two-target vowel in some but not necessarily all dialects.
3. rareA vowel digraph or ligature.

   The diphthong ae is sounded like ē (§7); that is, it has the sound of ey in they.

   1874, Theophilus Dwight Hall, A Child’s First Latin Book, John Murray, page 3

   2 more examples

   And he might have written the name, also, with the diphthong æ, as well as the single vowel, in the initial syllable, throughout all the preceding forms.

   1854, Robert Bigsby, Historical and Topographical Description of Repton, in the County of Derby, Woodfall and Kinder, page 47

   An improper diphthong has only one of the vowels sounded; as, ea in heat, oa in coal.

   1860, Joseph E. Worcester, An Elementary Dictionary of the English Language, Swan, Brewer, and Tileston, page 12