Source : Webster's Revised Unabridged Dictionary (1913)

Masterwort \Mas"ter*wort`\, n. (Bot.)
   (a) A tall and coarse European umbelliferous plant
       ({Peucedanum Ostruthium}, formerly {Imperatoria}).
   (b) The {Astrantia major}, a European umbelliferous plant
       with a showy colored involucre.
   (c) Improperly, the cow parsnip ({Heracleum lanatum}).

Source : WordNet®

Astrantia major
     n : European herb with aromatic roots and leaves in a basal tuft
         and showy compound umbels of white to rosy flowers [syn:
         {greater masterwort}]