The term UNDERWATER MENACE is composed of two crossword solutions, PIRANHA (7 letters) and SEADEVIL (8 letters). Piranhas are a species of freshwater fish that are native to South American rivers and are known for their sharp teeth and aggressive behavior. Seadevils are a type of anglerfish found in the deep sea, which have large mouths and long, whip-like tails. Both of these creatures can be considered underwater menaces due to their predatory nature.