The Collaborative International Dictionary of English v.0.48:

Pagan \Pa"gan\ (p[=a]"gan), n. [L. paganus a countryman,
   peasant, villager, a pagan, fr. paganus of or pertaining to
   the country, rustic, also, pagan, fr. pagus a district,
   canton, the country, perh. orig., a district with fixed
   boundaries: cf. pangere to fasten. Cf. Painim, Peasant,
   and Pact, also Heathen.]
   One who worships false gods; an idolater; a heathen; one who
   is neither a Christian, a Mohammedan, nor a Jew.
   [1913 Webster]

         Neither having the accent of Christians, nor the gait
         of Christian, pagan, nor man.            --Shak.
   [1913 Webster]

   Syn: Gentile; heathen; idolater.

   Usage: Pagan, Gentile, Heathen. Gentile was applied to
          the other nations of the earth as distinguished from
          the Jews. Pagan was the name given to idolaters in the
          early Christian church, because the villagers, being
          most remote from the centers of instruction, remained
          for a long time unconverted. Heathen has the same
          origin. Pagan is now more properly applied to rude and
          uncivilized idolaters, while heathen embraces all who
          practice idolatry.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pagan \Pa"gan\, a. [L. paganus of or pertaining to the country,
   pagan. See Pagan, n.]
   Of or pertaining to pagans; relating to the worship or the
   worshipers of false goods; heathen; idolatrous, as, pagan
   tribes or superstitions.
   [1913 Webster]

         And all the rites of pagan honor paid.   --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pagan
    adj 1: not acknowledging the God of Christianity and Judaism and
           Islam [syn: heathen, heathenish, pagan, ethnic]
    n 1: a person who does not acknowledge your god [syn: heathen,
         pagan, gentile, infidel]
    2: a person who follows a polytheistic or pre-Christian religion
       (not a Christian or Muslim or Jew)
    3: someone motivated by desires for sensual pleasures [syn:
       hedonist, pagan, pleasure seeker]

Moby Thesaurus II by Grady Ward, 1.0:

78 Moby Thesaurus words for "pagan":
   Gentile, Gothic, Philistine, allotheist, allotheistic, animist,
   animistic, atheist, atheistic, barbarous, bibliolatrous, bookless,
   chthonian, deceived, disbeliever, disbelieving, ethnic, faithless,
   fetishistic, functionally illiterate, gentile, grammarless,
   heathen, heathenish, hoodwinked, idol worshiping, idolater,
   idolatric, idolatrical, idolatrous, idolistic, ill-educated,
   illiterate, infidel, infidelic, led astray, lowbrow, minimifidian,
   misinformed, misinstructed, mistaught, nonbeliever,
   nonintellectual, nullifidian, paganish, paganistic,
   pagano-Christian, polytheist, polytheistic, profane, rude,
   secularist, unbeliever, unbelieving, unbooked, unbookish,
   unbooklearned, unbriefed, unchristian, uncultivated, uncultured,
   unedified, uneducated, unerudite, unguided, uninstructed,
   unintellectual, unlearned, unlettered, unliterary, unread,
   unrefined, unscholarly, unschooled, unstudious, untaught,
   untutored, zoolatrous