The Collaborative International Dictionary of English v.0.48:

Addiction \Ad*dic"tion\, n. [Cf. L. addictio an adjudging.]
   The state of being addicted; devotion; inclination. "His
   addiction was to courses vain." --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

addiction
    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: an abnormally strong craving
    3: (Roman law) a formal award by a magistrate of a thing or
       person to another person (as the award of a debtor to his
       creditor); a surrender to a master; "under Roman law
       addiction was the justification for slavery"

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "addiction":
   a habit, acquired tolerance, acute alcoholism, addictedness,
   alcoholism, amphetamine withdrawal symptoms, barbiturate addiction,
   barbiturism, chain smoking, chronic alcoholism, cocainism, crash,
   craving, dependence, dipsomania, drug addiction, drug culture,
   drug dependence, habituation, nicotine addiction,
   physical dependence, psychological dependence, tolerance,
   withdrawal sickness, withdrawal symptoms