1. (noun)actinium, Ac, atomic number 89 a radioactive element of the actinide series; found in uranium ores Synonyms: atomic number 89, alternating current, actinium, alternating electric current
2. (noun)alternating current, AC, alternating electric current an electric current that reverses direction sinusoidally Synonyms: atomic number 89, alternating current, actinium, alternating electric current