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)

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "legume":
   algae, autophyte, bean, boll, bracken, brown algae, burr, capsule,
   climber, cod, conferva, confervoid, creeper, diatom, fern,
   follicle, fruits and vegetables, fucus, fungus, grapevine,
   green algae, gulfweed, herb, heterophyte, hull, husk, ivy, kelp,
   legumen, lentil, liana, lichen, liverwort, mold, moss, mushroom,
   parasite, parasitic plant, pea, pease cod, pericarp, perthophyte,
   phytoplankton, planktonic algae, plant families, pod, puffball,
   pulse, red algae, rockweed, rust, saprophyte, sargasso, sargassum,
   sea lentil, sea moss, sea wrack, seaweed, seed pod, seed vessel,
   seedbox, seedcase, silique, smut, succulent, toadstool, vetch,
   vine, wort, wrack