What does GRAIN mean?

noun

1. a relatively small granular particle of a substance“a grain of sand”
2. foodstuff prepared from the starchy grains of cereal grasses
3. the side of leather from which the hair has been removed
4. a weight unit used for pearls or diamonds: 50 mg or 1/4 carat
5. 1/60 dram; equals an avoirdupois grain or 64.799 milligrams
6. 1/7000 pound; equals a troy grain or 64.799 milligrams
7. dry seed-like fruit produced by the cereal grasses: e.g. wheat, barley, Indian corn
8. a cereal grass“wheat is a grain that is grown in Kansas”