The term 'Rat Relative' refers to three small rodents: the MOUSE, VOLE, and GERBIL. The MOUSE is a five-letter word, the VOLE is a four-letter word, and the GERBIL is a six-letter word. All three of these animals are related to rats, and they are all small mammals that live in burrows or tunnels. The MOUSE is the most common of the three, and it is found in many parts of the world. The VOLE is a small rodent that lives in grassy areas, while the GERBIL is a desert-dwelling rodent that is native to Africa and Asia.