The term 'strong metal' can be summarized by two crossword solutions: IRON (4 letters) and STEEL (5 letters). IRON is a chemical element that has been used by humans since ancient times. It is the most abundant element on Earth, making up much of the Earth's core. STEEL is an alloy of IRON and other elements, such as carbon, that is stronger and more durable than IRON. STEEL is widely used in construction, manufacturing, and other industries.