[ˈaktɪnʌɪd], (Noun)

Definitions:
- any of the series of fifteen metallic elements from actinium (atomic number 89) to lawrencium (atomic number 103) in the periodic table. They are all radioactive, the heavier members being extremely unstable and not of natural occurrence


Phrases:

Origin:
1940s: from actinium + -ide, on the pattern of lanthanide