Let's face it, it's almost impossible to say bismuthous even if you want to, so this shouldn't cause too many problems.
See? Not easy, is it?
Now try big bismuthous thief.
Bismuthous, as you will have realised, means to do with bismuth. And what's bismuth? It's a very very slightly radioactive (its half-life comes out as about a billion times the age of the universe) metallic element.
This neat image is from Wikipedia showing artificially grown bismuth crystal in a stairstep crystal structure, with a 1 cm3 cube of bismuth metal beside it.
Bismuth is not all that widely used, but it's been found useful in diarrhoea cures, to cure eye infections, and as an "internal deodorant", a thing of which I really wish to know as little as possible.
You can make a bismuthous pearly-looking pigment which is used in cosmetics. It's also used as a less-toxic substitute for lead in casting, toy soldiers, ammunition, and water systems.
Bismuthous is technically restricted to describing bismuth in the trivalent state.
Unfortunately bismuth's trivalent state is the common one.
Word Not To Use Today: bismuthous. No one's quite sure whether this word comes from the Arabic bi ismid, having the properties of antimony, or the German weisse masse, white mass, later Latinised to bisemutum.