Source : Webster's Revised Unabridged Dictionary (1913)

Symbiosis \Sym`bi*o"sis\, n. [NL., fr. Gr. ? a living together,
   ? to live together; ? with + ? to live.] (Biol.)
   The living together in more or less imitative association or
   even close union of two dissimilar organisms. In a broad
   sense the term includes parasitism, or

   {antagonistic, or antipathetic, symbiosis}, in which the
      association is disadvantageous or destructive to one of
      the organisms, but ordinarily it is used of cases where
      the association is advantageous, or often necessary, to
      one or both, and not harmful to either. When there is
      bodily union (in extreme cases so close that the two form
      practically a single body, as in the union of alg[ae] and
      fungi to form lichens, and in the inclusion of alg[ae] in
      radiolarians) it is called

   {conjunctive symbiosis}; if there is no actual union of the
      organisms (as in the association of ants with
      myrmecophytes),

   {disjunctive symbiosis}.