The Collaborative International Dictionary of English v.0.48:

Incubate \In"cu*bate\, v. i. & t. [imp. & p. p. Incubated; p.
   pr. & vb. n. Incubating.] [L. incubatus, p. p. incubare to
   lie on; pref. in- in, on + cubare to lie down. Cf. Cubit,
   Incumbent.]
   1. To sit, as on eggs for hatching; to brood; to brood upon,
      or keep warm, as eggs, for the purpose of hatching.
      [1913 Webster]

   2. To maintain (a living organism, such as microorganisms or
      a premature baby) under appropriate conditions, such as of
      temperature, humidity, or atmospheric composition, for
      growth; as, coliform bacteria grow best when incubated at
      37[deg] C..
      [PJC]

   3. To develop gradually in some interior environment, until
      fully formed; as, the ideas for his book were incubating
      for two years before he began to write.
      [PJC]