What is a stone, commonly flat, used to sharpen cutting tools; a whetstone; -- called also rubstone. Rub iron, an iron guard on a wagon body, against which a wheel rubs when cramped too much called?

rub — A stone, commonly flat, used to sharpen cutting tools; a whetstone; -- called also rubstone. Rub iron, an iron guard on a wagon body, against which a wheel rubs when cramped too much. (Webster's 1913.)