The Collaborative International Dictionary of English v.0.48:

Sedation \Se*da"tion\, n. [L. sedatio.]
   The act of calming, or the state of being calm. [R.] --Coles.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sedation
    n 1: a state of reduced excitement or anxiety that is induced by
         the administrative of a sedative agent
    2: the administration of a sedative agent or drug [syn:
       sedation, drugging]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "sedation":
   catalepsy, coma, encephalitis lethargica, high, lethargy,
   narcohypnosis, narcolepsy, narcoma, narcosis, narcotic stupor,
   narcotization, nod, shock, sleeping sickness, sopor, stupor, swoon,
   thanatosis, trance