In phonology, hiatus, diaeresis (/ d aɪ ˈ ɛr ə s ə s,-ˈ ɪər-/), or dieresis 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 .

In linguistics, an alternation is the phenomenon of a morpheme exhibiting variation in its phonological realization. Each of the various realizations is called an alternant.The variation may be conditioned by the phonological, morphological, and/or syntactic environment in which the morpheme finds itself. Alternations provide linguists with data that allow them to determine …