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.