monophthong
Concise Oxford English Dictionary © 2008 Oxford University Press:
monophthong /ˈmɒnəfθɒŋ, məˈnɒpθɒŋ/
▶noun Phonetics a vowel that has a single perceived auditory quality.
– derivatives
monophthongal adjective.
monophthongal adjective.
– origin C17: from Gk monophthongos, from monos ‘single’ + phthongos ‘sound’.
'monophthong' also found in these Oxford entries:

