Source : Webster's Revised Unabridged Dictionary (1913)

Pigweed \Pig"weed`\, n. (Bot.)
   A name of several annual weeds. See {Goosefoot}, and
   {Lamb's-quarters}.

Source : WordNet®

pigweed
     n 1: common weedy European plant introduced into North America;
          often used as a potherb [syn: {lamb's-quarters}, {wild
          spinach}, {Chenopodium album}]
     2: leaves sometimes used as potherbs; seeds used as cereal;
        southern United States to Central America; India and China
        [syn: {Amaranthus hypochondriacus}]
     3: leaves collected from the wild [syn: {lamb's-quarter}, {wild
        spinach}]