Definitions for "Triphthong"
A combination of three vowel sounds in a single syllable, forming a simple or compound sound; also, a union of three vowel characters, representing together a single sound; a trigraph; as, eye, -ieu in adieu, -eau in beau, are examples of triphthongs.
A single syllable consisting of three consecutive vowel sounds.
A group of three vowels in the same syllable. In Spanish, this only happens in cases of sinalefa (eg e hoy).