The Collaborative International Dictionary of English v.0.48:

Trifolium \Tri*fo"li*um\, n. [L., clover.] (Bot.)
   A genus of leguminous herbs with densely spiked flowers and
   usually trifoliate leaves; trefoil. There are many species,
   all of which are called clover. See Clover.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Trifolium
    n 1: any leguminous plant having leaves divided into three
         leaflets [syn: Trifolium, genus Trifolium]