gridiron (n.)

cooking utensil for broiling over a fire, early 14c., griderne, alteration (by association with iron) of gridire (late 13c.), a variant of gridil (see griddle). Confusion of "l" and "r" was common in Norman dialect. Also a medieval instrument of torture by fire. As the word for a U.S. football field, by 1896, for its lines.