The Collaborative International Dictionary of English v.0.48:

Ostrea \Os"tre*a\, n. [L., an oyster.] (Zool.)
   A genus of bivalve Mollusca which includes the true oysters.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Ostrea
    n 1: type genus of the family Ostreidae [syn: Ostrea, genus
         Ostrea]