The term FIRE BUG is a combination of two words, FIRE and BUG. The first word, FIRE, is a noun that refers to an uncontrolled burning of combustible material, such as wood or coal. The second word, BUG, is a noun that refers to an insect, usually one that is small and annoying. Together, the two words form the term FIRE BUG, which is used to refer to a person who deliberately sets fires. The crossword solution for this term is ANT, which is a small insect that is often seen in large numbers.