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.
Late Greek monophthongos : Greek mono-, mono- + Greek phthongos, sound.(American Heritage® Dictionary of the English Language, Fourth Edition)
From Ancient Greek μονόφθογγος (monophthongos), from μόνος (monos, "single") + φθόγγος (phthongos, "sound"). (Wiktionary)