- actinium, Ac, atomic number 89 - a radioactive element of the actinide series; found in uranium ores
--1 is a kind of chemical element, element
--1 is a substance of uranium ore - alternating current, AC - an electric current that reverses direction sinusoidally; "In the US most household current is AC at 60 cycles per second"
--2 is a kind of electricity, electrical energy