It's hiatuses. Actually, the folks at m-w make it really hard on you. They only list the plural (or inflected forms) when they think adding -s or -es isn't obvious. They list it if the plural takes any other form or if it's the same word (hiatus is also accepted). Here's who knew:
Now, on to today's trivia, which comes from the last thought I had at night. I have no idea why this catch phrase popped into my head, but it did, and I couldn't remember who spawned it. So now I pass the byproducts of my misfiring brain on to you to put together. Here's the question:
What 1980s TV character regularly uttered the catch phrase, "Trust me, I know what I'm doing"?