D defs.my
Entry 1 sense Webster, 1913

Milligram

/mĭl'-əg-rămˌ/ · Mil·li·gram · IPA /ˈmɪlɪɡɹæm/
01 n. A measure of mass and weight, in the metric system, being the thousandth part of a gram, very nearly equal to the weight of a cubic millime…
  1. 1.
    A measure of mass and weight, in the metric system, being the thousandth part of a gram, very nearly equal to the weight of a cubic millimeter of water, or .01543 of a grain avoirdupois.