FLINT

[noun] - (a piece of) very hard grey or black glassy stoneHouses in this part of the country are built of flint. [U]People in early times used flint tools.Archaeologists have discovered several flints (= pieces of flint used as tools) on the site. [C]A flint is also a piece of stone or metal used in a musket (= gun) to make it fire or in a cigarette lighter to produce a flame.The morning air was sharp as flint against their faces. [U]He has a heart like flint/as hard as flint (= He is very unkind). [U]