Slate
SLATE, noun
1. An argillaceous stone which readily splits into plates; argillite; argillaceous shist.
2. A piece of smooth argillaceous stone, used for covering buildings.
3. A piece of smooth stone of the above species, used for writing on.
SLATE, verb intransitive To cover with slate or plates of stone; as, to slate a roof. [It does not signify to tile.]