The Collaborative International Dictionary of English v.0.48:

Lucern \Lu"cern\, n. [F. luzerne.] (Bot.)
   A leguminous plant (Medicago sativa), having bluish purple
   cloverlike flowers, cultivated for fodder; -- called also
   alfalfa. [Written also lucerne.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Alfalfa \Al*fal"fa\, n. [Sp.] (Bot.)
   The lucern (Medicago sativa), a leguminous plant having
   bluish purple cloverlike flowers, and cultivated for fodder;
   -- so called in California, Texas, etc.
   [1913 Webster]

WordNet (r) 3.0 (2006):

alfalfa
    n 1: important European leguminous forage plant with trifoliate
         leaves and blue-violet flowers grown widely as a pasture
         and hay crop [syn: alfalfa, lucerne, Medicago sativa]
    2: leguminous plant grown for hay or forage

U.S. Gazetteer Counties (2000):

Alfalfa -- U.S. County in Oklahoma
   Population (2000):    6105
   Housing Units (2000): 2832
   Land area (2000):     866.649527 sq. miles (2244.611876 sq. km)
   Water area (2000):    14.794124 sq. miles (38.316603 sq. km)
   Total area (2000):    881.443651 sq. miles (2282.928479 sq. km)
   Located within:       Oklahoma (OK), FIPS 40
   Location:             36.702841 N, 98.333427 W
   Headwords:
    Alfalfa
    Alfalfa, OK
    Alfalfa County
    Alfalfa County, OK