Wordnet 3.0
NOUN (1)
1. 
 any of a series of radioactive elements with atomic numbers 89 through 103; 
[syn: actinoid, actinide, actinon]
WordNet (r) 3.0 (2006):
actinon
    n 1: any of a series of radioactive elements with atomic numbers
         89 through 103 [syn: actinoid, actinide, actinon]