Vowel hiatus
| Sound change and alternation | 
|---|
| Fortition | 
| Dissimilation | 
In phonology, hiatus (/haɪˈeɪtəs/ hy-AY-təs) or diaeresis (/daɪˈɛrəsɪs, -ˈɪər-/ dy-ERR-ə-siss, -EER-; also spelled dieresis or diæresis) describes the occurrence of two separate vowel sounds in adjacent syllables with no intervening consonant. When two vowel sounds instead occur together as part of a single syllable, the result is called a diphthong.