I would say an hiatus. "An" is used before a word beginning H if the first syllable of that word isn't stressed. So, for instance, "a history book" but "an historic occasion".
Doing a quick Google search I see this is now considered a convention rather than a rule and interestingly I notice that my grammar checker wants to change the two instances of "an" above to "a".
Welcome back, by the way.
I thought the convention was that one used 'an' when the word originated from French, where the initial H wasn't pronounced, as in "an Hotel".
But as language changes constantly, so the rules change too. Bloody good job, otherwise we'd still be talking like Chaucer...
