Peanuts is the name Boxey calls the daggit (dog) during a deleted scene from "Saga of a Star World".
The daggit is the exact same animal as Muffit, suggesting two things:
Original Series definition: a domesticated canine, e.g. dog (see: daggit)
Original Series definition: a term for a robot, such as Muffit II (TOS: "Saga of a Star World")