Real Dictionary

grit
uncountable noun: Grit is very small pieces of stone. It is often put on roads in winter to make them less slippery.
uncountable noun: If someone has grit, they have the determination and courage to continue doing something even though it is very difficult.

grit in American English
rough, hard particles of sand, stone, etc.
to cover with grit
to make a grating sound
intransitive verb: to make a scratchy or slightly grating sound, as of sand being walked on; grate
noun: abrasive particles or granules, as of sand or other small, coarse impurities found in the air, food, water, etc
transitive verb: to cause to grind or grate together

grit in British English
noun: small hard particles of sand, earth, stone, etc
verb: to clench or grind together (two objects, esp the teeth)