Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun actinium

1 sense of actinium

Sense 1
actinium, Ac, atomic number 89 -- (a radioactive element of the actinide series; found in uranium ores)
       => chemical element, element -- (any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter)