iridium
corrosion-proof rainbow metal
Today this word meansOne of the metals most resistant to corrosion. It occurs with platinum.
Tennant discovered it in 1803. Because the metal's salts colored each solution differently, he named it for Iris, goddess of the rainbow.
It is famous as evidence for the dinosaurs' extinction — iridium concentrated in the 66-million-year-old layer became a clue to the asteroid impact.