The crossword solution for the term 'WHAT MIGHT COST YOU AN ARM AND A LEG?' is PIRANH, a six-letter word. Piranhas are freshwater fish native to South America that are known for their sharp teeth and aggressive behavior. They have been known to attack humans, and can cause serious injury or even death. Therefore, the phrase 'what might cost you an arm and a leg?' is often used to refer to something that is very expensive or dangerous.