The Collaborative International Dictionary of English v.0.48:

Monism \Mon"ism\ (m[o^]n"[i^]z'm or m[=o]"n[i^]z'm), n. [From
   Gr. mo`nos single.]
   1. (Metaph.) That doctrine which refers all phenomena to a
      single ultimate constituent or agent; -- the opposite of
      dualism.
      [1913 Webster]

   Note: The doctrine has been held in three generic forms:
         matter and its phenomena have been explained as a
         modification of mind, involving an idealistic monism;
         or mind has been explained by and resolved into matter,
         giving a materialistic monism; or, thirdly, matter,
         mind, and their phenomena have been held to be
         manifestations or modifications of some one substance,
         like the substance of Spinoza, or a supposed unknown
         something of some evolutionists, which is capable of an
         objective and subjective aspect.
         [1913 Webster]

   2. (Biol.) See Monogenesis, 1.
      [1913 Webster]

   3. The doctrine that the universe is an organized unitary
      being or total self-inclusive structure.

            Monism means that the whole of reality, i.e.,
            everything that is, constitutes one inseparable and
            indivisible entirety. Monism accordingly is a
            unitary conception of the world. It always bears in
            mind that our words are abstracts representing parts
            or features of the One and All, and not separate
            existences. Not only are matter and mind, soul and
            body, abstracts, but also such scientific terms as
            atoms and molecules, and also religious terms such
            as God and world.                     --Paul Carus.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Monogenesis \Mon`o*gen"e*sis\, n. [Mono- + genesis.]
   1. Oneness of origin; esp. (Biol.), development of all beings
      in the universe from a single cell; -- opposed to
      polygenesis. Called also monism. --Dana. --Haeckel.
      [1913 Webster]

   2. (Biol.) That form of reproduction which requires but one
      parent, as in reproduction by fission or in the formation
      of buds, etc., which drop off and form new individuals;
      asexual reproduction. --Haeckel.
      [1913 Webster]

   3. (Biol.) The direct development of an embryo, without
      metamorphosis, into an organism similar to the parent
      organism; -- opposed to metagenesis. --E. van Beneden.
      [1913 Webster]

WordNet (r) 3.0 (2006):

monism
    n 1: the doctrine that reality consists of a single basic
         substance or element [ant: pluralism]