It’s hot, sticky, humid, sweaty. Time to dive, time to get wet, time to hurl yourself off a pier or quay or jetty or wharf or convenient boulder into a fresh cool lake. Lunge, take the plunge, splash: splunge.
Is that a word, splunge? It is now – but, more to the point, it has been for a couple of centuries. Oxford’s first citation is from 1839, but the quotation treats it as already existing: “Here are two real American words:—‘Sloping’—for slinking away; ‘Splunging’, like a porpoise.” Splunge shows up in various American books of the 1800s, especially works of fiction, and it always means just what it sounds like it means.
Which, by the way, is what? Oxford declares the origin to be “imitative,” but let’s be honest about what it’s imitating. Yes, you can say that splunging into water sounds like “splunge,” but you could as soon say it sounds like “plush” or “kaff” or any of quite a few other onomatopoeics. Splunge has a conventional form shaped by precedent: it imitates not just a sound, but another word – or, really, more than one word.
It draws on plunge, of course, which has been in English since at least the 1300s, and came from Norman French, which had had it at least a couple of centuries already by then; it probably traced ultimately to the same Latin root (meaning ‘lead’, as in the metal) that gives us plumb. (Lunge, incidentally, didn’t hit English until the 1700s, at first as a fencing term trimmed down from allonge.) But it got that initial s from somewhere too. Splash has been around since the late 1600s, and it was formed by adding s to plash, which has been around since at least the mid-1500s, so we already had a model to follow. Various other spl- words have hit the scene over the centuries, and roughly half of them have to do with something wet and messy; the remainder include some other words with similar expressive aspect, such as split and splendid. It only makes sense that we would take plunge and add an s; really, we were bound to take the leap sooner or later.
So, yes, diving into water – especially deep water – has a certain “splunge!” about it, but in part that’s because we’re used to such a thing being expressed by words of similar sound. Why not splunge where others have splunged before? It wouldn’t be the first time anyone had given in to pier pressure… I mean peer pressure, I’m sure. We could equally say dive or immerse (from Latin mergo, ‘I dive’), or if we wanted to imitate the act and sound we could call it weeooo-froosh or something like that. But, since splunge is available, like a body of deep cool water for leaping into on a hot day, and a suitable spot for jumping in, why not avail ourselves of it?