The Collaborative International Dictionary of English v.0.48:

Partisan \Par"ti*san\ (p[aum]r"t[i^]*zan), n. [F., fr. It.
   partigiano. See Party, and cf. Partisan a truncheon.]
   [Written also partizan.]
   1. An adherent to a party or faction; esp., one who is
      strongly and passionately devoted to a party or an
      interest. "The violence of a partisan." --Macaulay.
      [1913 Webster]

            Both sides had their partisans in the colony.
                                                  --Jefferson.
      [1913 Webster]

   2. (Mil.)
      (a) The commander of a body of detached light troops
          engaged in making forays and harassing an enemy.
      (b) Any member of such a corps.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Partisan \Par"ti*san\, a. [Written also partizan.]
   1. Adherent to a party or faction; especially, having the
      character of blind, passionate, or unreasonable adherence
      to a party; as, blinded by partisan zeal.
      [1913 Webster]

   2. (Mil.) Serving as a partisan in a detached command; as, a
      partisan officer or corps.
      [1913 Webster]

   Partisan ranger (Mil.), a member of a partisan corps.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Partisan \Par"ti*san\, n. [F. pertuisane, prob. fr. It.
   partigiana, influenced in French by OF. pertuisier to pierce.
   It was prob. so named as the weapon of some partisans, or
   party men. Cf. Partisan one of a corps of light troops.]
   A kind of halberd or pike; also, a truncheon; a staff.
   [1913 Webster]

         And make him with our pikes and partisans a grave.
                                                  --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

partisan
    adj 1: devoted to a cause or party [syn: partisan, partizan]
           [ant: nonpartisan, nonpartizan]
    n 1: a fervent and even militant proponent of something [syn:
         partisan, zealot, drumbeater] [ant: nonpartisan,
         nonpartizan]
    2: an ardent and enthusiastic supporter of some person or
       activity [syn: enthusiast, partisan, partizan]
    3: a pike with a long tapering double-edged blade with lateral
       projections; 16th and 17th centuries [syn: partisan,
       partizan]

Moby Thesaurus II by Grady Ward, 1.0:

193 Moby Thesaurus words for "partisan":
   Charley, Conservative, Democrat, Labourite, Maecenas, Republican,
   Tory, VC, Vietcong, Whig, abettor, acquaintance, adherent, admirer,
   advocate, aficionado, aggressive, alter ego, angel, antiblack,
   apologist, appendage, attendant, backer, bellicose, belligerent,
   best friend, biased, bickering, bigoted, bipartisan, biparty,
   blind, booster, bosom friend, brother, buff, bushfighter,
   bushwhacker, casual, casual acquaintance, cavaliere servente,
   champion, chauvinistic, close acquaintance, close friend, cohort,
   colored, combative, confidant, confidante, courtier, dangler,
   defender, denominational, dependence, dependent, devoted, devotee,
   die-hard, disciple, disputatious, divisive, doctrinaire, dogmatic,
   encourager, endorser, enthusiast, eristic, exponent, factional,
   factious, familiar, fan, fanatic, favorer, fellow, fellow creature,
   fellowman, flunky, follower, following, freedom, friend,
   friend at court, guerilla, guerrilla, hanger-on, heeler, henchman,
   homme de cour, influenced, inseparable friend, interested,
   intimate, involved, irascible, irregular, irritable, jaundiced,
   know-nothing, limited, litigious, lover, loyalist, mainstay,
   maintainer, maquis, maquisard, myopic, narrow, narrow-minded,
   neighbor, nonobjective, one-sided, opinionated, other self,
   paranymph, parasite, parochial, partial, party, party faithful,
   party hack, party man, party member, party wheelhorse, patriot,
   patron, pickup, polarizing, polemic, prejudiced, prepossessed,
   promoter, protagonist, public, pugnacious, pursuer, pursuivant,
   quarrelsome, racist, registered Democrat, registered Republican,
   regular, reliance, repository, resistance, resistance fighter,
   rooter, satellite, second, seconder, sectarian, sectary, sectional,
   sexist, shadow, short-sighted, shrewish, sider, sponsor, stalwart,
   standby, stooge, successor, superpatriotic, support, supporter,
   sustainer, swayed, sympathizer, tagtail, tail, tendentious,
   trainbearer, twisted, ultranationalist, underground,
   underground fighter, undetached, undispassionate, unneutral,
   unreasoning, upholder, votary, ward heeler, warped, well-wisher,
   wheelhorse, wrangling, xenophobic, zealot