Definitions of grain:

• noun:   the direction or texture of fibers found in wood or leather or stone or in a woven fabric

  Example: "Saw the board across the grain"

• noun:   foodstuff prepared from the starchy grains of cereal grasses
• noun:   a small hard particle

  Example: "A grain of sand"

• noun:   dry seedlike fruit produced by the cereal grasses: e.g. wheat, barley, Indian corn
• noun:   1/7000 pound; equals a troy grain or 64.799 milligrams
• noun:   1/60 dram; equals an avoirdupois grain or 64.799 milligrams
• noun:   used for pearls or diamonds: 50 mg or 1/4 carat
• verb:   paint (a surface) to make it look like stone or wood
• verb:   become granular
• verb:   form into grains
• verb:   thoroughly work in

  Example: "His hands were grained with dirt"

• name:  A surname (very rare: popularity rank in the U.S.: #72447)