Classical music lovers, on seeing this word, may think first of one of the best-quality labels in the business. (I used to fantasize about buying their entire catalogue.) In uncapitalized usage, this word is halfway to contronymic: it refers to two things that, while in some ways related in nature, are really quite different. In art and sacred things, nimbus names what is more commonly called a halo: that lambent circle sitting on a saint’s head (one sees no nimbus on bimbos – you’ll want to be there in the nimbus when the saints go marching in). It is often seen spoked like a motion picture reel, or even as a full-body glow such as on the Virgin of Guadalupe (she didn’t need a tanning bed, either!). In more mundane matters, however, nimbus refers to a rain cloud.
Funny to think that there are two contrasting things commonly depicted above people’s heads in cartoons – the one a golden ring indicating innocence, the other a dark cloud, perhaps raining, indicating a glum or bitter mood or state of fortune (perhaps getting a B minus) – that can both be called nimbus. Does either really seem to match the word? The glow is typically called halo now, which is less equivocal and has that air of heavenly breath in its saying, and that leaves nimbus for the clouds – but it’s no longer a formal meteorological designation by itself; it shows in compounds such as nimbostratus and cumulonimbus to indicate that the kind of cloud in question rains (though the rain may be virga, not necessarily of Guadalupe). But, again, does nimbus sound like rain? Rather more like distant thunder, perhaps, with just a last hiss of preciptation on the [s]. At least the shape of the word has some cloudiness or raininess to it in the n and m. And can you guess which language has lent us this word? Yes, of course. It’s classical, naturally.