actinium
/ækˈtɪnɪəm/noun
mass noun
- the chemical element of atomic number 89, a radioactive metallic element of the actinide series. It is rare in nature, occurring as an impurity in uranium ores. (Symbol:Ac)（化学元素）锕（符号：Ac）。
词源
early 20th cent.: from Greek aktis, aktin- 'ray' + -IUM.