The Collaborative International Dictionary of English v.0.48:

Sardius \Sar"di*us\, n. [L. sardius, lapis sardinus, Gr. ?, ?,
   ?. See Sard.]
   A precious stone, probably a carnelian, one of which was set
   in Aaron's breastplate. --Ex. xxviii. 17.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sardius
    n 1: a deep orange-red variety of chalcedony [syn: sard,
         sardine, sardius]