From Latin 'vocalis' (vocal), short for 'littera vocalis' (voice-letter) — a sound produced without obstruction.
A speech sound made with the vocal tract open, without constriction; a letter representing such a sound (a, e, i, o, u in English).
From Old French 'vouel' (modern French 'voyelle'), from Latin 'vōcālis' (sounding, vocal), specifically short for 'littera vōcālis' (vocal letter — a letter produced by the unobstructed voice), from 'vōx' (voice), from PIE *wekʷ- (to speak, to utter). A vowel is literally a 'voice-letter' — a speech sound produced by the voice alone, with the vocal tract open and no articulatory obstruction. The contrast with consonants is etymologically built in: Latin 'cōnsonāns' (consonant) means
The Latin grammatical pair 'vōcālis' (vowel) and 'cōnsonāns' (consonant) is a calque of Greek 'phōnēen' (sounding, voiced) and 'symphōnon' (sounding together). The Romans translated the Greek linguistic terms into Latin: a vowel makes a sound ('vōx') by itself, while a consonant 'sounds together' ('cōn-' + 'sonāre') with a vowel. The terminology encodes a phonetic observation: you