"Mach two" is a term used to describe the speed of an object that is two times the speed of sound. There are several synonyms that can be used to describe this velocity level. One of the most commonly used synonyms for "mach two" is supersonic, which refers to any speed that is faster than the speed of sound. Another synonym that can be used is "twice the speed of sound," which is a literal description of what "mach two" means. Some other synonyms include hypersonic, ultra-fast, and rapid. Each of these words can be used to describe objects or phenomena that move at high speeds, often at levels that are difficult for humans to comprehend.