Source : Webster's Revised Unabridged Dictionary (1913)

Fungus \Fun"gus\, n.; pl. L. {Fungi}, E. {Funguses}. [L., a
   mushroom; perh. akin to a doubtful Gr. ? sponge, for ?;if so,
   cf. E. sponge.]
   1. (Bot.) Any one of the Fungi, a large and very complex
      group of thallophytes of low organization, -- the molds,
      mildews, rusts, smuts, mushrooms, toadstools, puff balls,
      and the allies of each.

   Note: The fungi are all destitute of chorophyll, and,
         therefore, to be supplied with elaborated nourishment,
         must live as saprophytes or parasites. They range in
         size from single microscopic cells to systems of
         entangled threads many feet in extent, which develop
         reproductive bodies as large as a man's head. The
         vegetative system consists of septate or rarely
         unseptate filaments called hyph[ae]; the aggregation of
         hyph[ae] into structures of more or less definite form
         is known as the mycelium. See Fungi, in the Supplement.

   2. (Med.) A spongy, morbid growth or granulation in animal
      bodies, as the proud flesh of wounds. --Hoblyn.

Source : WordNet®

fungus
     n : a parasitic plant lacking chlorophyll and leaves and true
         stems and roots and reproducing by spores
     [also: {fungi} (pl)]