|Origin:||cealc, from Latin calx ' LIME12', from Greek chalix 'small stone'|
soft white or grey rock formed a long time ago from the shells of small sea animals [= limestone]:
2 also chalks [plural]AV
small sticks of a white or coloured substance like soft rock, used for writing or drawing:
a box of coloured chalks
a piece of chalk
writing in chalk on the blackboard
3 British English
completely different from each other:
The two brothers are as different as chalk and cheese.
They're like chalk and cheese, those two.