The Collaborative International Dictionary of English v.0.48:

Ventilation \Ven`ti*la"tion\, n. [L. ventilatio: cf. F.
   ventilation.]
   1. The act of ventilating, or the state of being ventilated;
      the art or process of replacing foul air by that which is
      pure, in any inclosed place, as a house, a church, a mine,
      etc.; free exposure to air.
      [1913 Webster]

            Insuring, for the laboring man, better ventilation.
                                                  --F. W.
                                                  Robertson.
      [1913 Webster]

   2. The act of refrigerating, or cooling; refrigeration; as,
      ventilation of the blood. [Obs.] --Harvey.
      [1913 Webster]

   3. The act of fanning, or winnowing, for the purpose of
      separating chaff and dust from the grain.
      [1913 Webster]

   4. The act of sifting, and bringing out to view or
      examination; free discussion; public exposure.
      [1913 Webster]

            The ventilation of these points diffused them to the
            knowledge of the world.               --Bp. Hall.
      [1913 Webster]

   5. The act of giving vent or expression. "Ventilation of his
      thoughts." --Sir H. Wotton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ventilation
    n 1: the act of supplying fresh air and getting rid of foul air
         [syn: ventilation, airing]
    2: a mechanical system in a building that provides fresh air;
       "she was continually adjusting the ventilation" [syn:
       ventilation, ventilation system, ventilating system]
    3: free and open discussion of (or debate on) some question of
       public interest; "such a proposal deserves thorough public
       discussion" [syn: public discussion, ventilation]
    4: the bodily process of inhalation and exhalation; the process
       of taking in oxygen from inhaled air and releasing carbon
       dioxide by exhalation [syn: breathing, external
       respiration, respiration, ventilation]