Definitions of chalk:

• noun:   a piece of chalk (or similar substance) used for writing on blackboards or other surfaces
• noun:   a pure flat white with little reflectance
• noun:   a soft whitish calcite
• noun:   amphetamine used in the form of a crystalline hydrochloride; used as a stimulant to the nervous system and as an appetite suppressant
• verb:   write, draw, or trace with chalk
• name:  A surname (rare: 1 in 100000 families; popularity rank in the U.S.: #12083)