The (fissile) isotope of uranium of mass number 235.
Origin
Early 20th century; earliest use found in Science. From actin- + -o- + uranium, after French actinuranium; so called because actinium results from the radioactive decay of this isotope.
Definition of actino-uranium in US English:
actino-uranium
nounˌaktɪnə(ʊ)jʊˈreɪnɪəm
Chemistry Physics historical
The (fissile) isotope of uranium of mass number 235.
Origin
Early 20th century; earliest use found in Science. From actin- + -o- + uranium, after French actinuranium; so called because actinium results from the radioactive decay of this isotope.