Source : Webster's Revised Unabridged Dictionary (1913)

Nonesuch \None"such`\, n.
   A person or thing of a sort that there is no other such;
   something extraordinary; a thing that has not its equal. It
   is given as a name to various objects, as to a choice variety
   of apple, a species of medic ({Medicago lupulina}), a variety
   of pottery clay, etc.

Shamrock \Sham"rock\, n. [L. seamrog, seamar, trefoil, white
   clover, white honeysuckle; akin to Gael. seamrag.] (Bot.)
   A trifoliate plant used as a national emblem by the Irish.
   The legend is that St. Patrick once plucked a leaf of it for
   use in illustrating the doctrine of the trinity.

   Note: The original plant was probably a kind of wood sorrel
         ({Oxalis Acetocella}); but now the name is given to the
         white clover ({Trifolium repens}), and the black medic
         ({Medicago lupulina}).

Medic \Med"ic\, n. [L. medica, Gr. ? (sc. ?) a kind of clover
   introduced from Media, from ? Median.] (Bot.)
   A leguminous plant of the genus {Medicago}. The black medic
   is the {Medicago lupulina}; the purple medic, or lucern, is
   {M. sativa}.

Source : WordNet®

Medicago lupulina
     n : prostrate European herb with small yellow flowers and curved
         black pods; naturalized in North America [syn: {black
         medick}, {hop clover}, {yellow trefoil}, {nonesuch clover}]