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.
'Second, he emphasizes the economic value of actinides and fission products in the spent fuel but does not acknowledge either economic or proliferation concerns.'
'The members of the first of these blocks are called the lanthanide elements, and those in the second are the actinides.'
noun, Chemistry.
1.
any element of the actinide series.
Origin:
actinide
1940s: from actinium + -ide, on the pattern of lanthanide.