Real Dictionary

tuatara in American English
either of two primitive, amphibious, lizardlike reptiles (Sphenodon punctatus or S. guntheri) of the SW Pacific, with a row of spines along the back and a well-developed third eye: they are the only rhynchocephalians still in existence
noun: a large, primarily nocturnal, lizardlike reptile, Sphenodon punctatum, of islands near the coast of New Zealand: the only surviving rhynchocephalian

tuatara in British English
noun: a greenish-grey lizard-like rhynchocephalian reptile, Sphenodon punctatus, occurring only on certain small islands near New Zealand: it is the sole surviving member of a group common in Mesozoic times