Definition of indeterminate vowel in English:

indeterminate vowel

noun

Phonetics
  • The vowel heard in “a moment ago”; a schwa /ə/

    • ‘One change was a tendency to reduce any short vowel in an unstressed syllable to a common indeterminate vowel.’
    • ‘Armenian has an indeterminate vowel, which sounds like the e in ‘laurel’; this appears as ë.’