IRIDIUM

iridium, Ir, atomic number

(noun) a heavy brittle metallic element of the platinum group; used in alloys; occurs in natural alloys with platinum or osmium

Source: WordNet® 3.1

Etymology

Noun

iridium (countable and uncountable, plural iridiums)

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

(countable) A single atom of this element.

Source: Wiktionary

I*rid"i*um, n. Etym: [NL., fr. L. iris, iridis, the rainbow. So called from the iridescence of some of its solutions. See Iris.] (Chem.)

Definition: A rare metallic element, of the same group as platinum, which it much resembles, being silver-white, but harder, and brittle, and indifferent to most corrosive agents. With the exception of osmium, it is the heaviest substance known, its specific gravity being 22.4. Symbol Ir. Atomic weight 192.5.

Note: Iridium usually occurs as a native alloy with osmium (iridosmine or osmiridium), which may occur alone or with platinum. Iridium, as an alloy with platinum, is used in bushing the vents of heavy ordnance. It is also used for the points of gold pens, and in a finely powdered condition (iridium black), for painting porcelain black.

Source: Webster’s Unabridged Dictionary 1913 Edition