The American Heritage® Dictionary of the English Language, 4th Edition
n. A southwest Asian perennial herb (Medicago sativa) having compound leaves with three leaflets and clusters of usually blue-violet flowers. It is widely cultivated as a pasture and hay crop.
n. A plant, Medicago sativa, grown as a pasture crop.
n. A type or breed of this plant.
the GNU version of the Collaborative International Dictionary of English
n. The lucern (Medicago sativa), a leguminous plant having bluish purple cloverlike flowers, and cultivated for fodder; -- so called in California, Texas, etc.
The Century Dictionary and Cyclopedia
n. The Spanish name of lucerne, Medicago sativa, and the common name under which the chief varieties of lucerne are known in the western United States.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. important European leguminous forage plant with trifoliate leaves and blue-violet flowers grown widely as a pasture and hay crop
n. leguminous plant grown for hay or forage
Word Usage
"It will probably be news to most readers that alfalfa -- the wonderful forage crop of the West, the producer of more gold than all the mines of the Klondike -- was in use so long ago, for the impression is pretty general that it is comparatively new; the fact is that it is older than the Christian era and that the name alfalfa comes from the Arabic and means "the best crop.""