1. A series of 15 radioactive chemical elements with atomic numbers 89 through 103, including uranium and plutonium, characterized by filling the 5f electron shell.
Usage: plural form; singular is actinide; chemistry and physics term; also called actinoid series

Examples

• The actinides are all radioactive and many are found in nature or produced artificially.
• Uranium and plutonium are the most well-known actinides.
• Scientists study the properties of actinides to understand nuclear chemistry.
• The actinides occupy a special place in the periodic table below the lanthanides.
• Many actinides have extremely long half-lives and remain dangerous for thousands of years.
• The discovery of new actinides has expanded our understanding of the periodic table.