(n.) a wave
The waves on the surface of the ocean used to be called waws.
So what happened to waws—and where did the waves come in? Well, true story: wave has only been used as a noun in this way in English since around the early 1500s. It has existed as a verb considerably longer, with the Old English root of the modern English word for ‘to wave’, wafian, recorded in texts dating from around the turn of the ninth century. Earlier still, we can trace the verb wave back through English’s Germanic roots to our ancient ancestor language, Proto-Indo-European. In PIE, a root form along the lines of *huebh– was used to mean ‘to move to and fro’ or ‘back and forth’ (which is also, FYI, the ultimate origin of the verb weave).
But things in language are never straightforward, and confusingly Old English had another very similar word, wagian, that was derived from an entirely different PIE root, wegh–, meaning simply to go, move, or progress (the origin of hotchpotch of words like way, via, voyage and vehicle).
It’s difficult to pin down what precisely the difference between wagian and wafian was in Old English, and it’s by no means unusual to see them both somewhat dismissively explained in Anglo-Saxon dictionaries as simply ‘to fluctuate’. But there seems to be a distinction in that while wafian was used to describe an intentional movement back and forward (like a wave with a hand), wagian described an unintentional, unstoppable, or unavoidable undulating movement—such as that made by an unsteady object, something about to fall over, or tellingly, a boat tossed around on rough seas.
Over time, the “f” in the middle of wafian became voiced, and the word slowly morphed into wave. Wagian, meanwhile, had a soft “g” sound in its middle and so it morphed into waw. That meant that it was waw, not wave, that was first attached to what we now know as the waves on a body of water in the early Middle English period.
Confusion between these two very closely related words soon followed, and as just another word for an uneven, back-and-forth movement, wave began to outpace waw in the language until all but replacing it in the sixteenth century. Waw clung on to existence for a time, however, and still today can be found in use in a handful of English dialect.
It’s also still to be found fossilized in a handful of (alas, equally obscure) words like williwaw, an old nautical word for a sudden squall.