from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A single vowel articulated without change in quality throughout the course of a syllable, as the vowel of English bed.
- n. Two written vowels representing a single sound, as oa in boat.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. 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, /aɪə/, the sound in the non-rhotic pronunciation of "pyre").
from the GNU version of the Collaborative International Dictionary of English
- n. A single uncompounded vowel sound.
- n. A combination of two written vowels pronounced as one; a digraph.
from The Century Dictionary and Cyclopedia
- n. A simple vowel-sound.
- n. A combination of two written vowels pronounced as one.
A monophthong, on the other hand, is a vowel sound that has the same sound throughout, like the/æ/sound in American English hat.
Putting the emphasis on the final syllable of Sotomayor is unnatural in English (which is why the president stopped doing it after the first time at his press conference), unlike my correspondent's simple preference for a monophthong over a diphthong, and insisting on an unnatural pronunciation is something we shouldn't be giving in to.
She's getting the Oklahoma monophthong -- mah, she says, for my, and raht, for right.
Monophthongization is the process of converting a diphthong to a monophthong (I’ll explain those terms in a minute.)