amphisbaena
A 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)
Where it comes from
From Latin amphisbaena, from Ancient Greek ἀμφίσβαινα (amphísbaina, from ἀμφίς (amphís, “both ways”) + βαίνω (baínō, “to go”)).
Adapted from the Wiktionary entry amphisbaena (CC BY-SA 4.0).