1.nounA mythical serpent having a head at each end of its body, able to move in either direction.
"1971: What do you call that animal that goes backward and forward, head at each end? —Amphisbaena. A kind of lizard. It doesn't exist. — Anthony Burgess, M/F (Penguin 2004, p. 109)"
2.nounA member of a genus of lizards, native to the Americas, having extremities which are very similar.