...from Merriam-Webster OnLine:

"Main Entry:        vow·el
Pronunciation:        'vau(-&)l
Function:        noun
Etymology:        Middle English, from Middle French vouel, from Latin vocalis -- more at VOCALIC
1 : one of a class of speech sounds in the articulation of which the oral part of the breath channel is not blocked and is not constricted enough to cause audible friction; broadly : the one most prominent sound in a syllable
2 : a letter or other symbol representing a vowel -- usually used in English of a, e, i, o, u, and sometimes y "

A vowel is a sound first, the symbol for that sound second.