le mot du jour

This past week it seems like everything has been roiling. Not rolling, not boiling, but roiling. The word has appeared at least thrice in the Times in the last seven days, usually to refer to the economy or the financial markets.
The Webster defines it thus: ROIL-"make turbid by stirring up the sediment or dregs of" or "to move turbulently : be in a state of turbulence or agitation". So kind of like roll, kind of like boil, but chock full of its own special significance and shades of meaning. Where did this unlikely verb come from? Chances are it was probably coined in the late 1500s, inspired by rouiller, French for "to rust, make muddy."
Don't you love words you know that student of English as a second language will ever learn?