In phonetics and phonology, a triphthong is a monosyllabic sound which functions as a single phoneme. It is actually a sequence of three distinct sounds each having its own quality, though it is most of the time regarded as a single sound, i.e. as some kind of vowel.
Most of the time, the first sound (onset) and the last sound (coda) of a triphthong are real vowels, while the second sound (nucleus) is rather a semivowel, as in aua. A triphthong may also consist of two semivowels with a real vowel in between, as in iei.
Triphthongs occur in the phoneme inventory of many languages. In English, they can be heard in words such as hour and fire. In Spanish, sound sequences such as iai and iei are very common. However, it is the phonetic context (i.e. whether the vowels are closed or open, whether the first vowel is tonic or not) which determines if these sequences are articulated as triphtongs or as combinations of a single vowel and a diphthong with a hiatus in between. In Punjabi, the triphthong aaiaa is itself a lexeme meaning "came". The triphthong oiiaa also occurs in this language, for example in rassooiiaa which means "cook".
- T.K. Bathia, Punjabi: A Cognitive-Descriptive Grammar (2003): 341