I speak a couple of languages extremely remedially, so I know enough to know that the root "mor-" almost always means "death" in some capacity. In this case it actually translates to "to bite," meaning it helps synthetic indigo dye that much of the fashion industry uses to bite onto the fabric with its VICIOUS JAWS OF DEATH. Just kidding. But seriously, these things are really toxic. Some mordants are acidic, but clothing companies most commonly use mordants made from metals like chromium or aluminum. The latter is slightly safer than chrome, but both kill off plants exposed to factory waste water, destroy ecosystems, poison drinking water, and generally are awful. They are, though, why your jeans fade so perfectly while your t-shirts just eventually all equalize to the same shade of puce or mauve or some other tone reached after five-plus years of the sweat-sun-wash cycle.