1. A series of 15 radioactive chemical elements with atomic numbers 89 to 103, including uranium and plutonium; also called the actinide series.
Usage: plural of actinoid; chemistry term; sometimes spelled 'actinides' in modern usage

Examples

• The actinoids are all radioactive and occur naturally or are produced artificially.
• Uranium and thorium are the most abundant actinoids found in Earth's crust.
• Scientists study the properties of actinoids to understand nuclear chemistry.
• The actinoids occupy the bottom row of the periodic table's f-block.
• Plutonium is one of the synthetic actinoids created in nuclear reactors.