St. Elmo's FIRE is a weather phenomenon caused by a corona discharge from a sharp object in an electrical field. It is named after St. Erasmus of Formia, the patron saint of sailors, who was said to protect sailors and their ships from storms with a mysterious light. The term St. Elmo's FIRE refers to the visible electrical discharge that appears as a blue or violet glow around the object. The four-letter crossword solution for St. Elmo's FIRE is 'FIRE'.