The Collaborative International Dictionary of English v.0.48:

Legume \Leg"ume\ (l[e^]g"[-u]m or l[-e]*g[=u]m"), n. [F.
   l['e]gume, L. legumen, fr. legere to gather. So called
   because they may be gathered without cutting. See Legend.]
   1. (Bot.) A pod dehiscent into two pieces or valves, and
      having the seed attached at one suture, as that of the
      pea.
      [1913 Webster]

   Note: In the latter circumstance, it differs from a siliqua,
         in which the seeds are attached to both sutures. In
         popular use, a legume is called a pod, or cod; as, pea
         pod, or peas cod.
         [1913 Webster]

   2. pl. The fruit of leguminous plants, as peas, beans,
      lupines; pulse.
      [1913 Webster]

WordNet (r) 3.0 (2006):

legume
    n 1: an erect or climbing bean or pea plant of the family
         Leguminosae [syn: legume, leguminous plant]
    2: the fruit or seed of any of various bean or pea plants
       consisting of a case that splits along both sides when ripe
       and having the seeds attach to one side of the case
    3: the seedpod of a leguminous plant (such as peas or beans or
       lentils)