bas·i·lo·saur·us 
(băs′ə-lə-sôrəs)
(băs′ə-lə-sôrəs)n.
A large extinct whale of the genus Basilosaurus of the Eocene Epoch, having a long thin body and vestigial hind limbs.
[New Latin Basilosaurus, genus name : Greek basileus, king + Greek sauros, lizard (from its former classification as a reptilian).]