Duba was the name an African tribe used for the Nandi bear.
The Fourth Doctor called it a "legendary" bear. The Doctor promised to hunt the duba for the tribe after Mposi was killed. Instead, he and his companions escaped, and the tribe killed their chief for helping them escape. After the tribe and the TARDIS left the scene, a duba approached the chief's dead body. (PROSE: To Kill a Nandi Bear)