synérèse

Synérèse, also spelled sinéresis or sinerese, is a phonological process in some Romance languages and in French in which two adjacent vowels that would normally form a hiatus are pronounced as a single syllable. This merging reduces the syllable count of the affected word or phrase, typically by forming a diphthong or a single vocalic nucleus.

The concept is contrasted with hiatus, the pronunciation of two consecutive vowels in separate syllables. The realization and status of synérèse vary across languages, dialects, and historical periods. In poetry and prosody, synérèse is often discussed as a device that allows poets to adjust meter and line length; its acceptability can differ by stylistic tradition and era. In some languages, sinéresis may be a productive phonological tendency in everyday speech, while in others it is chiefly a literary or regional feature.

In contemporary descriptions, the term is used with language-specific details: it is common in discussions of Spanish, Portuguese, and related varieties under the label sinéresis; in French phonology the same term denotes the coalescence of vowel sounds within or across syllables. The process is typically erosion of distinct syllabic boundaries and can influence the syllable count of poetry and the phonetic interpretation of words.

Etymology traces to Greek syn- “together” and hairesis “choosing” (via French synérèse). See also hiatus, elision, diphthong.