i ‧ rid ‧ i ‧ um /ɪˈrɪdiəm/ BrE AmE noun [uncountable]
[ Date: 1800-1900 ; Language: Latin ; Origin: iris ( ⇨ ↑ iris ); because when it becomes liquid in a particular acid, it shows the colors of the rainbow ]
a hard and very heavy metal that is combined with ↑ platinum to make jewellery and is used in scientific instruments. It is a chemical ↑ element : symbol Ir