The Collaborative International Dictionary of English v.0.48:

Sclerotium \Scle*ro"ti*um\, n.; pl. Sclerotia. [NL., fr. Gr.
   sklhro`s hard.]
   1. (Bot.) A hardened body formed by certain fungi, as by the
      Claviceps purpurea, which produces ergot.
      [1913 Webster]

   2. (Zool.) The mature or resting stage of a plasmodium.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ergot \Er"got\, n. [F. ergot, argot, lit., a spur.]
   1. A diseased condition of rye and other cereals, in which
      the grains become black, and often spur-shaped. It is
      caused by a parasitic fungus, Claviceps purpurea.
      [1913 Webster]

   2. The mycelium or spawn of this fungus infecting grains of
      rye and wheat. It is a powerful remedial agent, and also a
      dangerous poison, and is used as a means of hastening
      childbirth, and to arrest bleeding.
      [1913 Webster]

   3. (Far.) A stub, like soft horn, about the size of a
      chestnut, situated behind and below the pastern joint.
      [1913 Webster]

   4. (Anat.) See 2d Calcar, 3
      (b) .
          [1913 Webster]

WordNet (r) 3.0 (2006):

Claviceps purpurea
    n 1: a fungus that infects various cereal plants forming compact
         black masses of branching filaments that replace many
         grains of the plant; source of medicinally important
         alkaloids and of lysergic acid [syn: ergot, Claviceps
         purpurea]