1) A small hard biscuit; probably so called from the noise it emits when broken. The word seems to be peculiar to the United States.
The following anecdote was related to me by the Hon. Albert Gallatin. When travelling in England with his family in 1818, he stopped at an inn and ordered a servant to bring them some "crackers and cheese" for their lunch. But what was his surprise to see the servant return with a plate of cheese and half a dozen nut-crackers!
2) A nick-name applied to the backwoodsmen of Georgia.
3) (FIRE-CRACKER) A little paper cylinder filled with powder or combustible matter, imported from China. It receives its name from the noise it produces in exploding. In England it is called a squib.