From WordNet (r) 3.0 (2006):
chalk
n 1: a soft whitish calcite
2: a pure flat white with little reflectance
3: an amphetamine derivative (trade name Methedrine) used in the
form of a crystalline hydrochloride; used as a stimulant to
the nervous system and as an appetite suppressant [syn:
methamphetamine, methamphetamine hydrochloride,
Methedrine, meth, deoxyephedrine, chalk, chicken
feed, crank, glass, ice, shabu, trash]
4: a piece of calcite or a similar substance, usually in the
shape of a crayon, that is used to write or draw on
blackboards or other flat surfaces
v 1: write, draw, or trace with chalk