ˈ ̷ ̷ˌ ̷ ̷ noun
Etymology: Middle English firston, from Old English fȳrstān, from fȳr fire + stān stone — more at fire , stone
1. : pyrite formerly used for striking fire ; also : flint
2. : a stone that will endure high heat and is used especially for lining furnaces and kilns — used especially of a sandstone occurring in the south of England
3. : a plate of iron covering the front of the furnace in a slag hearth except for a few inches of space between it and the bedplate