A vocal, or sometimes a whispered, sound modified by resonance in the oral passage, the peculiar resonance in each case giving to each several vowel its distinctive character or quality as a sound of speech; -- distinguished from a consonant in that the latter, whether made with or without vocality, derives its character in every case from some kind of obstructive action by the mouth organs. Also, a letter or character which represents such a sound. See Guide to Pronunciation, §§ 5, 146-149.
One of the two main classes of speech sounds (which also includes diphthongs and triphthongs) in the articulation of which the breath channel is not blocked and not restricted so as to cause friction. A vowel is the most prominent part in a syllable. Examples: /a/, /e/, /i/, /o/, /u/. Complementary term: consonant.