Everyone is familiar with the hippopotamus, the gargantuan gray pachyderm that's cute but can also be dangerous and deadly. The word hippopotamus has one of my favorite etymologies. It's not that it's esoteric or complex. It comes from the Greek hippo- meaning horse and potam- meaning river, so literally, it means "river horse." There's something oddly funny to me about thinking about a hippopotamus as a river horse, but such is language. There are a number of hippo- words in addition to this that are equally amusing, baffling, or fascinating.
Case in point: hippotigrine, meaning "of or relating to the zebra." Etymologically, however, this means "horse tiger." It's definitely amusing to think of a zebra not as its own animal, but as a hybrid of a tiger and a horse. It's funny, but it makes sense--the zebra does, after all, look like a horse, but with striped patterns reminiscent of the tiger.
Then, of course, there's hippogriff. It's a mythical creature that's half griffin and half horse. That one's straightforward enough, but I still love it because of its portmanteau-style construction. There are plenty of other very straightforward hipp- words, like hippology (the study of horses), hippic (relating to horses or horse racing), and hippodrome (a stadium for horse races). Overall, though, it's a fun (although common) root that has a part in some incredible words.