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]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "inhalation":
   Aqua-Lung, air current, artificial respiration, aspiration,
   asthmatic wheeze, breath, breath of air, breathing, broken wind,
   cough, crosscurrent, current, current of air, downdraft, draft,
   exhalation, expiration, exsufflation, fall wind, flow of air,
   following wind, gasp, gulp, hack, head wind, hiccup, indraft,
   inflow, inhalator, inhalement, inrush, inspiration, insufflation,
   iron lung, jetstream, katabatic wind, monsoon,
   mouth-to-mouth resuscitation, movement of air, oxygen mask,
   oxygen tent, pant, puff, respiration, scuba, sigh, sneeze, sniff,
   sniffle, snore, snoring, snuff, snuffle, sternutation, stertor,
   stream, stream of air, suck, sucking, suction, suspiration,
   tail wind, undercurrent, updraft, wheeze, wind