a unanimous vote vs an undergraduate

[Kooper]

Does anyone know why we put "a" before "unanimous" but "an" before "undergraduate"?

I think both of them start with a vowel and the vowel is not emphasized. Why do they use different indefinite article?

[technobabel]

This is a good time for somebody to invoke the timeless maxim which is: "It's the expeption that proves the rule."

My wildest guess is that too many people tried to pronounce "an unanimous" and it just doesn't feel right. Native speakers do acknowledge those rules but don't always follow them wholeheartedly.

[Wayne]

When the initial "u" is pronounced like the "u" in "cute" (it starts with a semi-vowel as the "y" in "yes"), the indefinite article to be used is an "a", whereas when the "u" is pronounced like the "u" in "cut" (a shrt vowel sound), the indefinite article to be used is an "an".