Definition of: vowel

(vou′əl) noun
1. Phonet. A voiced speech sound produced by the relatively unimpeded passage of air through the mouth, altering in quality according to the shape of the resonance cavity: distinguished from consonant. Vowels may be characterized by the height of the tongue (high, mid, low), the place of articulation (front, central, back), the tension of the tongue muscles (tense, lax), and the presence of lip rounding; as, (ōo) is a high, back, tense, rounded vowel.
2. A letter indicating such a sound, as a, e, i, o, or u.
—adjective Of or pertaining to a vowel; vocal, [<OF vouele <L vocalis (littera) vocal (letter) <vox, vocis a voice, sound. Doublet of VOCAL.]