chalk
n. C / Un. a soft, white or colored stick used for writing or drawing on hard surfaces like blackboards. It is made from a type of soft limestone.
n. a soft, white, porous sedimentary carbonate rock, or a stick of this material used for writing on non-porous surfaces. Often used in educational or athletic contexts for marking.
The teacher uses white chalk to write on the board.
Gymnasts often apply powdered chalk to their hands to improve their grip and prevent slipping during a routine.
The artist used various shades of pastel chalk to create a temporary mural on the sidewalk, knowing the rain would eventually wash the vibrant colors away.
From Middle English chalk, chalke, from Old English ċealc, from Proto-West Germanic *kalk, borrowed from Latin calx (“limestone”), again borrowed from Ancient Greek χάλιξ (khálix, “pebble”). Doublet of calx and cauk.
Uncountable when referring to the rock or the substance; countable when referring to individual sticks used for writing.