How do you say “monophthong” in Vietnamese?

Vietnamese words for “monophthong”

• nguyên âm đơnListennoun
  Hanoi [ŋwiən˧˧ ʔəm˧˧ ʔɗəːn˧˧] · Saigon [ŋwiəŋ˧˧ ʔəm˧˧ ʔɗəːŋ˧˧]nguyên level âm level đơn level

  monophthong

  for “monophthong” meaning: 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 oppose