noun.
A unit of mass equal to one thousandth (10−3) of a gram.
The Century Dictionary and Cyclopedia
noun.
The thousandth part of a gram, equal to 0.015432, + or about , of a grain.
the GNU version of the Collaborative International Dictionary of English
noun.
A measure of weight, in the metric system, being the thousandth part of a gram, equal to the weight of a cubic millimeter of water, or .01543 of a grain avoirdupois.
noun.
An SI unit of mass, equivalent to one thousandth of a gram. Symbol: mg
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
one thousandth (1/1,000) gram
Word Usage
"While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M&M candy)."