Fire powder is a term used to describe an explosive mixture of potassium nitrate, sulfur, and charcoal. It was first used in the 13th century and is the earliest known form of gunpowder. The two crossword solutions for the term FIRE POWDER are ASHES (5 letters) and ASH (3 letters). ASHES are the remains of something that has been burned, and ASH is a light-colored powdery residue left after something has been burned.