Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

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