What is a word of one syllable containing one vowel sound called?

A word of one syllable that contains one vowel sound is termed a monosyllable. This term is derived from the Greek roots "mono," meaning one, and "syllable," referring to a unit of pronunciation. Monosyllabic words are often characterized by their simplicity and brevity, making them foundational in language development and phonemic awareness.

In contrast, polysyllables contain two or more syllables, which inherently includes multiple vowel sounds. Diphthongs refer to complex vowel sounds that begin with one vowel sound and glide into another within the same syllable, complicating the phonetic structure beyond that of a simple monosyllable. Trisyllables are words that contain three syllables, and again, this designation includes multiple vowel sounds. Therefore, the term monosyllable appropriately identifies a word that is singular in both syllable count and vowel sound.