The Collaborative International Dictionary of English v.0.48:

Inhalation \In`ha*la"tion\, n. [Cf. F. inhalation.]
   The act of inhaling; also, that which is inhaled.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inhalation
    n 1: the act of inhaling; the drawing in of air (or other gases)
         as in breathing [syn: inhalation, inspiration,
         aspiration, intake, breathing in]
    2: a medication to be taken by inhaling it [syn: inhalant,
       inhalation]