The Collaborative International Dictionary of English v.0.48:

Habituation \Ha*bit`u*a"tion\ (h[.a]*b[i^]t"[-u]*[=a]"sh[u^]n),
   n. [Cf. F. habituation.]
   The act of habituating, or accustoming; the state of being
   habituated.
   [1913 Webster]

WordNet (r) 3.0 (2006):

habituation
    n 1: being abnormally tolerant to and dependent on something
         that is psychologically or physically habit-forming
         (especially alcohol or narcotic drugs) [syn: addiction,
         dependence, dependance, dependency, habituation]
    2: a general accommodation to unchanging environmental
       conditions

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "habituation":
   a habit, acclimation, acclimatization, accommodation, accustoming,
   acquired tolerance, acute alcoholism, adaption, addictedness,
   addiction, adjustment, alcoholism, amphetamine withdrawal symptoms,
   barbiturate addiction, barbiturism, breaking, breaking-in,
   case hardening, chain smoking, chronic alcoholism, cocainism,
   conditioning, crash, craving, dependence, dipsomania,
   domestication, drug addiction, drug culture, drug dependence,
   familiarization, hardening, housebreaking, inurement,
   naturalization, nicotine addiction, orientation,
   physical dependence, psychological dependence, seasoning, taming,
   tolerance, training, withdrawal sickness, withdrawal symptoms