Some two-letter words are ordinary and banal, while others are obscure but ultimately aggravating, and finally there are those that are both obscure and gratifying. In this last category we find ai, a variety of three-toed sloth native to South America. When it comes to three-toed sloths there are only four kinds. You’ve got your pygmies, your pale-throats and your brown-throats, and your maned sloths. That’s what an ai is. File it away for future reference; it is in knowing such things that we find the gratification previously mentioned.
Also of note: ai takes no letter in front to form a three-letter word, the first such word we’ve encountered in this listing.
From the rear it takes seven: aid, ail, aim, ain, air, ais and ait. Most of these are familiar, and I assume ais is the plural of ai. As for ain, that looks like Scots to me, meaning “own.” That leaves ait, which refers to an island in a river. It’s obscure and chiefly British and used mostly for islands in the Thames, but this seems like a word that deserves to be more widely deployed. Anyone who’s enjoyed a riparian island knows they have a special character all their own; it only stands to reason they should have a name.