ˈgrīn(d)zˌtōn, -)ˌstōn, archaic or dial ˈgrinztən or -in(t)st- noun
Etymology: Middle English grindston, from grinden to grind + ston stone — more at grind , stone
1.
a. : millstone 1
b. : a flat circular stone of natural sandstone that revolves on an axle and is used for grinding tools or shaping or smoothing objects
2. : stone suitable for grindstones