The Collaborative International Dictionary of English v.0.48:

Naturalization \Nat`u*ral*i*za"tion\, n. [Cf. F.
   naturalisation.]
   The act or process of naturalizing, esp. of investing an
   alien with the rights and privileges of a native or citizen;
   also, the state of being naturalized.
   [1913 Webster]

WordNet (r) 3.0 (2006):

naturalization
    n 1: the quality of being brought into conformity with nature
         [syn: naturalization, naturalisation]
    2: the proceeding whereby a foreigner is granted citizenship
       [syn: naturalization, naturalisation]
    3: the introduction of animals or plants to places where they
       flourish but are not indigenous [syn: naturalization,
       naturalisation]
    4: changing the pronunciation of a borrowed word to agree with
       the borrowers' phonology; "the naturalization in English of
       many Italian words" [syn: naturalization, naturalisation]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "naturalization":
   Americanization, about-face, acclimation, acclimatization,
   accommodation, acculturation, accustoming, adaption, adjustment,
   admission, adoption, affiliation, alchemy, assimilation,
   assumption, becoming, breaking, breaking-in, case hardening,
   change, change-over, citizenship by naturalization,
   citizenship papers, conditioning, conversion, culture shock,
   domestication, familiarization, flip-flop, growth, habituation,
   hardening, housebreaking, inurement, lapse, nationalization,
   naturalized citizenship, orientation, papers, passage, progress,
   re-formation, reconversion, reduction, resolution, reversal,
   seasoning, shift, switch, switch-over, taming, training,
   transformation, transit, transition, turning into, volte-face