/ ˈvaʊəl; NAmE / noun ( phonetics )
1.
a speech sound in which the mouth is open and the tongue is not touching the top of the mouth, the teeth, etc., for example /ɑ:, e, ɔ:/ :
vowel sounds
Each language has a different vowel system.
—see also cardinal vowel
2.
a letter that represents a vowel sound. In English the vowels are a, e, i, o, and u.
—compare consonant
—see also diphthong
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WORD ORIGIN
Middle English : from Old French vouel , from Latin vocalis (littera) vocal (letter).