A vowel (in the sense of a sound rather than a letter of the alphabet) that has the same sound throughout its pronunciation, such as the short vowels in ""pap"", ""pep"", ""pip"", ""pop"" and ""pup"", as opposed to a diphthong (eg, /aɪ/, the vowel in ""pipe"") or a triphthong (eg, /aɪÉ/, the sound in the non-rhotic pronunciation of ""pyre"").