- a steel-gray, rare metallic element, belonging to the platinum group of metals. Symbol: Ru; atomic weight: 101.07; atomic number: 44; specific gravity: 12.2 at 20°C.
- a hard brittle white element of the platinum metal group. It occurs free with other platinum metals in pentlandite and other ores and is used to harden platinum and palladium. Symbol: Ru; atomic no: 44; atomic wt: 101.07; valency: 0–8; relative density: 12.41; melting pt: 2334°C; boiling pt: 4150°C
