Inenubilable

The Latin word for cloud was nubes and, as a result, some eighteenth century classicist invented the lovely word enubilate, which meant to blow the mists and fogs away and to make something clear. It's rather like elucidate or clarify, just much prettier.

Then, in the twentieth century, a journalist went further and invented the utterly wonderful word inenubilable for something that cannot be enubilated. Inenubilable can be applied to problems, mysteries, enigmas and other dark conundrums.

It may also be applied to cities that are incurably mist-laden, like London today. Or as Max Beerbohm put it in Zuleika Dobson:

There is nothing in England to be matched with what lurks in the vapours of these meadows, and in the shadows of these spires—that mysterious, inenubilable spirit, spirit of Oxford.

And there are three more lovely book covers up at bookhugger.co.uk.