Real Dictionary

vowel
countable noun: A vowel is a sound such as the ones represented in writing by the letters 'a', 'e', 'i', ' o', and 'u', which you pronounce with your mouth open, allowing the air to flow through it. Compare consonant.

vowel in American English
any voiced speech sound characterized by generalized friction of the air passing in a continuous stream through the pharynx and opened mouth but with no constriction narrow enough to produce local friction; the sound of the greatest prominence in most syl
of a vowel or vowels
noun: a speech sound produced without occluding, diverting, or obstructing the flow of air from the lungs (opposed to consonant)

vowel in British English
noun: a voiced speech sound whose articulation is characterized by the absence of friction-causing obstruction in the vocal tract, allowing the breath stream free passage. The timbre of a vowel is chiefly determined by the position of the tongue and the lips