SLATE

noun

1. A fine-grained homogeneous sedimentary rock composed of clay or volcanic ash which has been metamorphosed so that it cleaves easily into thin layers.
2. The bluish-grey colour of most slate.
3. A chalkboard, sheet of slate for writing on with chalk or with a thin rod of slate (a slate pencil) formerly commonly used by both students and teachers in schools

adjective

1. Having the bluish-grey/gray colour of slate.