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1. A single vowel articulated without change in quality throughout the course of a syllable, as the vowel of English bed.
2. Two written vowels representing a single sound, as oa in boat.
[Late Greek monophthongos : Greek mono-, mono- + Greek phthongos, sound.]
mon′oph·thon′gal (-thông′gəl, -thŏng′-) adj.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Phonetics & Phonology) a simple or pure vowel
[C17: from Greek monophthongos, from mono- + thongos sound]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
mon•oph•thong(ˈmɒn əfˌθɔŋ, -ˌθɒŋ)
a vowel sound retaining the same quality throughout its duration. Compare diphthong (def. 1).
[1610–20; < Greek monóphthongos=mono- mono- + phthóngos sound]
mon′oph•thon`gal (-gəl) adj.
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