chalk

1. (uncountable) A soft, white, powdery limestone (calcium carbonate, CaCO₃).Examples: "chalk cliffs are not recommended for climbing"uncountable

2. (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).Examples: "the chalk used to write on the blackboard makes a squeaky sound"countable

3. (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).Examples: "when working out your next move, it's a good idea to get some more chalk from the bag"uncountable

4. (US, military, countable) A platoon-sized group of airborne soldiers.UScountable

5. (US, sports, chiefly basketball, horse racing) The favorite in a sporting event.UScountableuncountable

6. (US, sports, chiefly basketball) The prediction that there will be no upsets, and the favored competitor will win.Examples: "OK, let's get rid of the chalk players right away. The chalk likes North Carolina. Dean Smith has taken Carolina to the Final Four six times."; "Excuse us for sticking with the chalk, but the predicted winners are Afternoon Deelites in the Derby, Oliver McCall over Larry Holmes, Nick Faldo in the Masters, and Al Unser Jr. in the Grand Prix."; "Instead, he played the chalk and selected the No. 1 overall seed in the tournament."UScountableuncountable