The Collaborative International Dictionary of English v.0.48:

Incubation \In`cu*ba"tion\, n. [L. incubatio: cf. F.
   incubation.]
   [1913 Webster]
   1. A sitting on eggs for the purpose of hatching young; a
      brooding on, or keeping warm, (eggs) to develop the life
      within, by any process. --Ray.
      [1913 Webster]

   2. (Med.) The development of a disease from its causes, or
      its period of incubation. (See below.)
      [1913 Webster]

   3. A sleeping in a consecrated place for the purpose of
      dreaming oracular dreams. --Tylor.
      [1913 Webster]

   4. The maintenance (of a living organism, such as
      microorganisms or a premature baby) in appropriate
      conditions, such as of temperature, humidity, or
      atmospheric composition, for growth.
      [PJC]

   5. The gradual development in some interior environment,
      until fully formed; as, the incubation time for developing
      a new drug may be longer than ten years from its first
      discovery.
      [PJC]

   Period of incubation, or Stage of incubation (Med.), the
      period which elapses between exposure to the causes of an
      infectious disease and the attack resulting from it; the
      time during which an infective agent must grow in the body
      before producing overt symptoms of disease.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

incubation
    n 1: maintaining something at the most favorable temperature for
         its development
    2: (pathology) the phase in the development of an infection
       between the time a pathogen enters the body and the time the
       first symptoms appear
    3: sitting on eggs so as to hatch them by the warmth of the body
       [syn: brooding, incubation]