The Collaborative International Dictionary of English v.0.48:

Generation \Gen`er*a"tion\, n. [OE. generacioun, F.
   g['e]n['e]ration, fr.L. generatio.]
   1. The act of generating or begetting; procreation, as of
      animals.
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   2. Origination by some process, mathematical, chemical, or
      vital; production; formation; as, the generation of
      sounds, of gases, of curves, etc.
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   3. That which is generated or brought forth; progeny;
      offspiring.
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   4. A single step or stage in the succession of natural
      descent; a rank or remove in genealogy. Hence: The body of
      those who are of the same genealogical rank or remove from
      an ancestor; the mass of beings living at one period;
      also, the average lifetime of man, or the ordinary period
      of time at which one rank follows another, or father is
      succeeded by child, usually assumed to be one third of a
      century; an age.
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            This is the book of the generations of Adam. --Gen.
                                                  v. 1.
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            Ye shall remain there [in Babylon] many years, and
            for a long season, namely, seven generations.
                                                  --Baruch vi.
                                                  3.
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            All generations and ages of the Christian church.
                                                  --Hooker.
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   5. Race; kind; family; breed; stock.
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            Thy mother's of my generation; what's she, if I be a
            dog?                                  --Shak.
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   6. (Geom.) The formation or production of any geometrical
      magnitude, as a line, a surface, a solid, by the motion,
      in accordance with a mathematical law, of a point or a
      magnitude; as, the generation of a line or curve by the
      motion of a point, of a surface by a line, a sphere by a
      semicircle, etc.
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   7. (Biol.) The aggregate of the functions and phenomene which
      attend reproduction.
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   Note: There are four modes of generation in the animal
         kingdom: scissiparity or by fissiparous generation,
         gemmiparity or by budding, germiparity or by germs, and
         oviparity or by ova.
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   Alternate generation (Biol.), alternation of sexual with
      asexual generation, in which the products of one process
      differ from those of the other, -- a form of reproduction
      common both to animal and vegetable organisms. In the
      simplest form, the organism arising from sexual generation
      produces offspiring unlike itself, agamogenetically.
      These, however, in time acquire reproductive organs, and
      from their impregnated germs the original parent form is
      reproduced. In more complicated cases, the first series of
      organisms produced agamogenetically may give rise to
      others by a like process, and these in turn to still other
      generations. Ultimately, however, a generation is formed
      which develops sexual organs, and the original form is
      reproduced.

   Spontaneous generation (Biol.), the fancied production of
      living organisms without previously existing parents from
      inorganic matter, or from decomposing organic matter, a
      notion which at one time had many supporters; abiogenesis.
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The Collaborative International Dictionary of English v.0.48:

Spontaneous \Spon*ta"ne*ous\ (sp[o^]n*t[=a]"n[-e]*[u^]s), a. [L.
   spontaneus, fr. sponte of free will, voluntarily.]
   1. Proceeding from natural feeling, temperament, or
      disposition, or from a native internal proneness,
      readiness, or tendency, without constraint; as, a
      spontaneous gift or proposition.
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   2. Proceeding from, or acting by, internal impulse, energy,
      or natural law, without external force; as, spontaneous
      motion; spontaneous growth.
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   3. Produced without being planted, or without human labor;
      as, a spontaneous growth of wood.
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   Spontaneous combustion, combustion produced in a substance
      by the evolution of heat through the chemical action of
      its own elements; as, the spontaneous combustion of waste
      matter saturated with oil.

   Spontaneous generation. (Biol.) See under Generation.
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   Syn: Voluntary; uncompelled; willing.

   Usage: Spontaneous, Voluntary. What is voluntary is the
          result of a volition, or act of choice; it therefore
          implies some degree of consideration, and may be the
          result of mere reason without excited feeling. What is
          spontaneous springs wholly from feeling, or a sudden
          impulse which admits of no reflection; as, a
          spontaneous burst of applause. Hence, the term is also
          applied to things inanimate when they are produced
          without the determinate purpose or care of man.
          "Abstinence which is but voluntary fasting, and . . .
          exercise which is but voluntary labor." --J. Seed.
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                Spontaneous joys, where nature has its play,
                The soul adopts, and owns their firstborn away.
                                                  --Goldsmith.
          [1913 Webster] -- Spon*ta"ne*ous*ly, adv. --
          Spon*ta"ne*ous*ness, n.
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WordNet (r) 3.0 (2006):

spontaneous generation
    n 1: a hypothetical organic phenomenon by which living organisms
         are created from nonliving matter [syn: abiogenesis,
         autogenesis, autogeny, spontaneous generation]