noun

• (uncountable) A soft, white, powdery limestone (calcium carbonate, CaCO₃).
  "chalk cliffs are not recommended for climbing"
• (countable) A piece of chalk, or nowadays processed compressed gypsum (calcium sulfate, CaSO₄), that is used for drawing and for writing on a blackboard (chalkboard).
  "the chalk used to write on the blackboard makes a squeaky sound"
• (uncountable, climbing, gymnastics) A white powdery substance used to prevent hands slipping from holds when climbing, or losing grip in weight-lifting or gymnastics, sometimes but not always limestone-chalk, often magnesium carbonate (MgCO₃).
  "when working out your next move, it's a good idea to get some more chalk from the bag"
• (US, military, countable) A platoon-sized group of airborne soldiers.

verb

• (figurative) To record a score or event, as if on a chalkboard.
  "This Book it chaulketh out before thine eyes / The man that ſeeks the everlaſting Prize: / It ſhevvs you vvhence he comes, vvhither he goes, / VVhat he leaves undone; alſo vvhat he does: / It alſo ſhovvs you hovv he runs, and runs, / Till he unto the Gate of Glory comes."