naturalization

n. conferral of citizenship rights, process of becoming a citizen; process of acclimation (also naturalisation)

For the biology usage, see Naturalisation (biology) and Invasive species. In law, naturalization refers to an act whereby a person acquires a citizenship different from that person's citizenship at birth. Naturalization is most commonly associated with economic migrants or refugees who have immigrated to a country and resided there as aliens, and who have voluntarily and actively chosen to become citizens of that country after meeting specific requirements. However, naturalization that is at least passive, and often not voluntary, can take place upon annexation or border adjustments between countries. Unless resolved by denaturalization or renunciation of citizenship, naturalization can lead to multiple citizenship.
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Noun
1. the quality of being brought into conformity with nature
(synonym) naturalisation
(hypernym) naturalness
(derivation) domesticate, cultivate, naturalize, naturalise, tame
2. the proceeding whereby a foreigner is granted citizenship
(synonym) naturalisation
(hypernym) proceeding, legal proceeding, proceedings
(derivation) naturalize, naturalise
(classification) law, jurisprudence
3. the introduction of animals or plants to places where they flourish but are not indigenous
(synonym) naturalisation
(hypernym) introduction, debut, first appearance, launching, unveiling, entry
(derivation) domesticate, cultivate, naturalize, naturalise, tame
4. changing the pronunciation of a borrowed word to agree with the borrowers' phonology; "the naturalization in English of many Italian words"
(synonym) naturalisation
(hypernym) borrowing, adoption
(derivation) naturalize, naturalise

(n.)
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.
  

The conferring of nationality of a state upon a person after birth, by any means whatsoever. 8 USC

The act by which an alien is made a citizen of the United States of America.

The Constitution of the United States, Art. I, vests in Congress the power " to establish an uniform rule of naturalization." In pursuance of this authority Congress have passed several laws on this subject.