monophthong

from The Collaborative International Dictionary of English v.0.48

Monophthong \Mon"oph*thong\, n. [Gr. ? with one sound; mo`nos
   alone + ? sound, voice.]
   1. A single uncompounded vowel sound.
      [1913 Webster]

   2. A combination of two written vowels pronounced as one; a
      digraph.
      [1913 Webster]