Answers taken from this Quora thread.
Ennui
What it means: A lack of spirit, enthusiasm, or interest.
How you may have pronounced it: N-U-I.
How it's actually pronounced: ON-wee.
NBC
Aspartame
What it means: A low-calorie sweetener.
How you may have pronounced it: As-part-a-may.
How it's actually pronounced: ass-PAR-tame.
Fox
Dour
What it means: Silent and gloomy.
How you may have pronounced it: Maybe you thought it sounded like the word "sour"?
How it's actually pronounced: It rhymes with "tour."
Disney
Quinoa
What it means: An herb.
How you may have pronounced it: kwin-o-a.
How it's actually pronounced: KEEN-wa.
Warner Bros.
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17 Words You've Probably Been Pronouncing Wrong For Years