Wordnet 3.0
NOUN (1)
1. 
 (virology) a complete viral particle; 
 nucleic acid and capsid (and a lipid envelope in some viruses); 
WordNet (r) 3.0 (2006):
virion
    n 1: (virology) a complete viral particle; nucleic acid and
         capsid (and a lipid envelope in some viruses)