Source : Webster's Revised Unabridged Dictionary (1913)

Lambkill \Lamb"kill`\, n. (Bot.)
   A small American ericaceous shrub ({Kalmia angustifolia}); --
   called also {calfkill}, {sheepkill}, {sheep laurel}, etc. It
   is supposed to poison sheep and other animals that eat it at
   times when the snow is deep and they cannot find other food.

Source : WordNet®

lambkill
     n : North American dwarf shrub resembling mountain laurel but
         having narrower leaves and small red flowers; poisonous
         to young stock [syn: {sheep laurel}, {pig laurel}, {Kalmia
         angustifolia}]