pound-mass noun1 •A unit of mass equal to the weight, on earth (subject to standard gravity), of a mass of one avoirdupois pound, equal to about 453.592 grams. Symbol lbm or lbₘ.On the moon, however the weight of a pound-mass (lb or lbm) is only about one sixth of a pound-force (lbf). — 2000 formspounds-mass
