Source : Webster's Revised Unabridged Dictionary (1913)

Motherwort \Moth"er*wort`\, n. (Bot.)
   (a) A labiate herb ({Leonurus Cardiaca}), of a bitter taste,
       used popularly in medicine; lion's tail.
   (b) The mugwort. See {Mugwort}.

Source : WordNet®

motherwort
     n : bitter Old World herb of hedgerows and woodland margins
         having toothed leaves and white or pale pink flowers
         [syn: {Leonurus cardiaca}]