"Dinosaur" was the name the Twelfth Doctor gave to the supposed language spoken by dinosaurs, or at least by Tyrannosaurus Rex. After an unusually enormous T. Rex was inadvertently brought to Victorian London when it swallowed the TARDIS, the Doctor had a few words with the creature upon exiting the TARDIS, which the Tyrannosaur had coughed up, before passing out due to strain from his most recent regeneration. Later, after climbing onto a rooftop, he attempts to carry on a conversation with the Tyrannosaur, only to watch in horror as the Half-Face Man incinerated the dinosaur, having somehow extracted part of its optic nerve unnoticed.
While it is possible that no such language exists and the Twelfth Doctor was joking, or that he was suffering from the extreme confusion caused by his recent regeneration, unlike the Eleventh Doctor's claims to speak the languages of babies and horses, which were played for laughs, the Twelfth Doctor's claim of speaking Dinosaur was for the most part taken at face value by Clara Oswald and the Paternoster Gang, and at least once, Clara seems genuinely convinced that the Doctor is translating the roars and moans of the T. Rex as it wanders around the Thames. (TV: Deep Breath)