The crossword solution for the term PROMISING CLUE is LEAD, which is a four-letter word. LEAD is a chemical element with the symbol Pb and atomic number 82. It is a heavy metal that is denser than most common materials. LEAD has been used since ancient times, primarily in plumbing and roofing materials. In more recent times, LEAD has been used in paint, batteries, and ammunition. LEAD is also used in some industrial processes, such as smelting and soldering. LEAD is toxic to humans and animals, so its use is now regulated in many countries.