iridium

noun

Etymology: From international scientific vocabulary, from New Latin iridium, from Classical Latin iris + -ium, from Ancient Greek ἶρις (îris, “rainbow”), because of the bright colour of many of the element's salts.

1. A chemical element with an atomic number of 77: a very hard, brittle, silvery-white transition metal of the platinum group.

   “Iridium is extremely rare on the surface of the earth but much more common in meteorites.”

2. A single atom of this element.