The Collaborative International Dictionary of English v.0.48:

Citizen \Cit"i*zen\, n. [OE. citisein, OF. citeain, F. citoyen,
   fr. cit['e] city. See City, and cf. Cit.]
   1. One who enjoys the freedom and privileges of a city; a
      freeman of a city, as distinguished from a foreigner, or
      one not entitled to its franchises.
      [1913 Webster]

            That large body of the working men who were not
            counted as citizens and had not so much as a vote to
            serve as an anodyne to their stomachs. --G. Eliot.
      [1913 Webster]

   2. An inhabitant of a city; a townsman. --Shak.
      [1913 Webster]

   3. A person, native or naturalized, of either sex, who owes
      allegiance to a government, and is entitled to reciprocal
      protection from it.
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   Note: This protection is . . . national protection,
         recognition of the individual, in the face of foreign
         nations, as a member of the state, and assertion of his
         security and rights abroad as well as at home. --Abbot
         [1913 Webster]

   4. One who is domiciled in a country, and who is a citizen,
      though neither native nor naturalized, in such a sense
      that he takes his legal status from such country.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Citizen \Cit"i*zen\, a.
   1. Having the condition or qualities of a citizen, or of
      citizens; as, a citizen soldiery.
      [1913 Webster]

   2. Of or pertaining to the inhabitants of a city;
      characteristic of citizens; effeminate; luxurious. [Obs.]
      [1913 Webster]

            I am not well,
            But not so citizen a wanton as
            To seem to die ere sick.              --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

citizen
    n 1: a native or naturalized member of a state or other
         political community [ant: alien, foreigner,
         noncitizen, outlander]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "citizen":
   burgess, burgher, citizen by adoption, civilian, cosmopolitan,
   cosmopolite, deditician, denizen, dweller, franklin, free citizen,
   freedman, freedwoman, freeman, freewoman, householder, hyphenate,
   hyphenated American, immigrant, inhabitant, metic, national,
   native, naturalized citizen, nonbelligerent, noncombatant,
   nonnative citizen, nonresistant, nonresister, oppidan, ratepayer,
   resident, subject, taxpayer, towner, townsman, townswoman,
   villager, voter



Bouvier's Law Dictionary, Revised 6th Ed (1856):

CITIZEN, persons. One who, under the constitution and laws of the United
States, has a right to vote for representatives in congress, and other
public officers, and who is qualified to fill offices in the gift of the
people. In a more extended sense, under the word citizen, are included all
white persons born in the United States, and naturalized persons born out of
the same, who have not lost their right as such. This includes men, women,
and children.
     2. Citizens are either native born or naturalized. Native citizens may
fill any office; naturalized citizens may be elected or appointed to any
office under the constitution of the United States, except the office of
president and vice-president. The constitution provides, that "the citizens
of each state shall be entitled to all the privileges and immunities of
citizens in the several states." Art. 4, s. 2.
     3. All natives are not citizens of the United States; the descendants
of the aborigines, and those of African origin, are not entitled to the
rights of citizens. Anterior to the adoption of the constitution of the
United States, each state had the right to make citizens of such persons as
it pleased. That constitution does not authorize any but white persons to
become citizens of the United States; and it must therefore be presumed that
no one is a citizen who is not white. 1 Litt. R. 334; 10 Conn. R. 340; 1
Meigs, R. 331.
     4. A citizen of the United States, residing in any state of the Union,
is a citizen of that state. 6 Pet. 761 Paine, 594;1 Brock. 391; 1 Paige, 183
Metc. & Perk. Dig. h.t.; vide 3 Story's Const. Sec. 1687 Bouv. Inst. Index,
b. t.; 2 Kent, Com. 258; 4 Johns. Ch. R. 430; Vatt. B. 1, c. Id, Sec. 212;
Poth. Des Personnes, tit. 2, s. 1. Vide Body Politic; Inhabitant.