Triphthongs  

Very rarely, the nucleus of a single syllable may contain three vowel sounds that quickly glide together; these sounds are known as triphthongs.

There are three triphthongs that are generally agreed upon in American English: /aʊə/ (“ah-oo-uh”), /aɪə/ (“ah-ih-uh”), and /jʊə/ (“ee-oo-uh”). These always come before an R sound in a word.

There is some disagreement among linguists as to whether the first two are truly triphthongs, or if they are simply two syllables that are merged closely together (/aʊ.ə/ and /aɪ.ə/). As we look at examples of each of the possible triphthongs below, we’ll consider them as both single and double syllables. (For the purposes of this section, a syllable break will be indicated by a dot [ . ].)

This vowel sound occurs when the digraph “OU” is followed by an “R.”

This triphthong is pronounced with the letter combination “IRE.”

In addition to “IRE” words, there are a few other specific instances where this pronunciation may occur:

This triphthong sometimes occurs when the digraph “UR” comes after a hard consonant and is followed by an E, Y, or I. Rather than breaking up the sound into two syllables like the previous two triphthongs, this one is often rounded to leave out the schwa altogether.