What the meaning of slate?

An argillaceous rock which readily splits into thin plates; argillite; argillaceous schist., Any rock or stone having a slaty structure., A prepared piece of such stone., A thin, flat piece, for roofing or covering houses, etc., A tablet for writing upon., An artificial material, resembling slate, and used for the above purposes., A thin plate of any material; a flake., A list of candidates, prepared for nomination or for election; a list of candidates, or a programme of action, devised beforehand., To cover with slate, or with a substance resembling slate; as, to slate a roof; to slate a globe., To register (as on a slate and subject to revision), for an appointment., To set a dog upon; to bait; to slat. See 2d Slat, 3.