Medical Definition of grain
1a: a seed or fruit of a cereal grassb: the seeds or fruits of various food plants including the cereal grasses and in commercial and statutory usage other plants (as the soybean)c: plants producing grain
2: a small hard particle or crystal (as of sand or salt)
3: a unit of avoirdupois, Troy, and apothecaries' weight equal to 0.0648 gram or 0.002286 avoirdupois ounce or 0.002083 Troy ounce—abbreviation gr
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