Quite a long time ago — about a thousand years, in fact — if you lived in the British Isles and did something foolish, you’d be called “dusilec,” or “dyslíc.” That’s a word that’s been obsolete for quite a long time too, so long that even one of its derivatives doesn’t make sense to us any more. The derivative was “dusischip” — which was used in relation to “dusilec” the same way “silliness” is similar to “silly.”
These words are so old the few surviving citations are very difficult to decipher these days; they tend to be things like “Nis bute dusilec al þæt ha driueð”, or “Swe folc dysig,” which aren’t particularly helpful unless you’ve studied ancient languages. Nor is their origin especially interesting; they come from Old Frisian, which is so old most people have never heard of it. There is a modern version of Frisian still spoken on a couple of Dutch islands in the North Sea, though. They’re the Frisian Islands.
So we’re left with the only interesting aspects of “dusilec” and “dusischip,” and those have to do with what happened when they disappeared. Like many words that faded from common use, they morphed into something a bit different. English speakers — and for that matter, maybe speakers of any language — often tend to use shorter versions of words just for convenience. Around the mid 1300s, where once you might have said (and written) “dusilec” or “dyslic,” “dysy” began to be what you’d employ: “Than waxes his hert hard and hevy. And his heved feble and dysy.” (1340).
By 1581, this became “disie”: “For feare they be disie when they daunce.” And by 1653, something we recognize had finally emerged: “ They were so exceeding dizzy in the head that they would fall down.” From then on, “dizzy” was the winner, even if Shakespeare did spell it “dizi” in 1608’s King Lear: “How feareful And dizi tis to cast ones eyes so low.”
The only fork in the road was the word “duzzy”, which for some reason meant hard of hearing: “‘E’s lother duzzy; e doesna ‘ear very well.” This doesn’t seem to be all that closely related to the centuries of usage of “dizzy,” even though its sound does seem closer to the original “dusilec.” It also sounds a bit like “dunny” and “dunch,” both of which used to mean deaf. But none of those three were ever particularly widely used, and nobody seems to have any idea where they came from. “Dunny” had a number of other meanings — it was at first just a shade of brown — but none of those have anything to do with sound or hearing. Maybe it was just a case of duzzy people mishearing something, after which ensued this whole dizzying linguistic saga.
