A chain reactor is a device that uses nuclear reactions to generate energy. There are several synonyms for this term, including nuclear reactor, atomic reactor, and fission reactor. These terms are often used interchangeably to refer to the same device. Other synonyms for chain reactor include breeder reactor, which is a type of reactor that produces more fuel than it consumes, and pressurized water reactor, which is a common type of nuclear reactor used in power plants. Overall, chain reactor is a fairly specific term that refers to a particular type of device, but there are many other synonyms that can be used to describe similar technologies and processes.