DON'T spoil it by posting the answer right away. Please wait at least 24 hours.
It is not obscure; it is a perfectly ordinary, common English word. There are no tricks here. "Vowel" means one of the five letters <em>a</em>, <em>e</em>, <em>i</em>, <em>o</em>, or <em>u</em>. It does not contain either of the letters <em>w</em> or <em>y</em>. It's not a logic puzzle or a wording trick.