slate

1. (uncountable, geology) A fine-grained homogeneous sedimentary rock composed of clay or volcanic ash which has been metamorphosed so that it cleaves easily into thin layers.Examples: "Some of the minor Welsh 2 ft. gauge railways, we hear from Mr. N. F. G. Dalston, are enjoying a miniature boom owing to the demand for slate for the repair of damaged roofs."; "The Penrhyn slate quarry possibly dates back to the sixteenth century, as it appears that in 1580 Sion Tudor asked the Bishop of Bangor for a shipload of slate."uncountable

2. (uncountable) The bluish-grey colour of most slate.Synonyms: slate blue, slate grey, slate grayuncountable

3. (countable) 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.Examples: "He wrote all down one side of the slate and all up the other, and then remarked--"As there's no time to finish that, The time has come to have our chat.""countable

4. (countable) A roofing-tile made of slate.Examples: "In 1765 only 80 men were employed, and the annual output of slates did not exceed 1,000 tons, and large-scale quarrying was not begun by Lord Penrhyn until 1782."; "The necessary works were extensive and included replacing missing and damaged slates and other roof repairs (in order to make the building watertight), pointing and drainpipe replacement, and extensive replacement of rotten floorboarding."countable

5. (countable) A record of money owed.Examples: "Put it on my slate – I’ll pay you next week."Synonyms: account, bill, tabcountable

6. (countable, chiefly US) A list of affiliated candidates for an election.Examples: "Ice is one of a slate of young, idealistic candidates for Move Forward who have joined mainstream politics in the hope that this election allows Thailand to break the cycle of military coups […]"UScountable