noun
: a deliquescent salt FeCl 3 that is obtained in anhydrous form (as by heating iron in chlorine) as dark crystals appearing red by transmitted light and green by reflected light, that forms several crystalline hydrates (as the yellow hexahydrate FeCl 3 .6H 2 O), and that is used chiefly as an oxidizing agent, as a catalyst, as an etching agent in photoengraving, as a coagulant in treating industrial wastes, and in medicine in a water solution or tincture usually as an astringent or styptic; iron trichloride