The Collaborative International Dictionary of English v.0.48:

Adherent \Ad*her"ent\, a. [L. adhaerens, -entis, p. pr.: cf. F.
   adh['e]rent.]
   1. Sticking; clinging; adhering. --Pope.
      [1913 Webster]

   2. Attached as an attribute or circumstance.
      [1913 Webster]

   3. (Bot.) Congenitally united with an organ of another kind,
      as calyx with ovary, or stamens with petals.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Adherent \Ad*her"ent\, n.
   1. One who adheres; one who adheres; one who follows a
      leader, party, or profession; a follower, or partisan; a
      believer in a particular faith or church.
      [1913 Webster]

   2. That which adheres; an appendage. [R.] --Milton.
      [1913 Webster]

   Syn: Follower; partisan; upholder; disciple; supporter;
        dependent; ally; backer.
        [1913 Webster]

WordNet (r) 3.0 (2006):

adherent
    adj 1: sticking fast
    n 1: someone who believes and helps to spread the doctrine of
         another [syn: disciple, adherent]

Moby Thesaurus II by Grady Ward, 1.0:

181 Moby Thesaurus words for "adherent":
   Averroist, Berkeleian, Cartesian, Comtist, Cynic, Cyrenaic,
   Eleatic, Epicurean, Eretrian, Fichtean, Hegelian, Heideggerian,
   Heraclitean, Herbartian, Humist, Husserlian, Kantian,
   Kierkegaardian, Leibnizian, Marxist, Megarian, Neo-Hegelian,
   Neo-Pythagorean, Neoplatonist, Parmenidean, Peripatetic, Platonist,
   Pyrrhonist, Pythagorean, Sartrian, Scholastic, Scotist, Socratist,
   Sophist, Spencerian, Spinozist, Stoic, Thomist, Wittgensteinian,
   adhesive, agnostic, animist, appendage, applauder, appreciator,
   attendant, backer, barnacle, booster, bramble, brier, buff,
   bulldog, burr, cavaliere servente, cement, champion, claqueur,
   cohort, commender, cosmotheist, courtier, creature, dangler, decal,
   decalcomania, deist, dependent, dialectical materialist, disciple,
   dualist, dummy, eclectic, egoist, empiricist, encomiast,
   essentialist, eulogist, eulogizer, existentialist, extoller, fan,
   figurehead, flunky, follower, following, gillie, glue, goon, gunk,
   hanger-on, hedonist, heeler, henchman, homme de cour, humanist,
   hylomorphist, hylotheist, hylozoist, idealist, immaterialist,
   individualist, intuitionist, jackal, lackey, lauder, leech, limpet,
   logical empiricist, man, materialist, mechanist, mentalist, minion,
   molasses, monist, mucilage, myrmidon, mystic, naturalist,
   nominalist, ontologist, organic mechanist, organicist, panegyrist,
   panpsychist, pantheist, parasite, partisan, paste, physicist,
   plaster, plugger, positivist, pragmatist, praiser, prickle,
   promoter, psychist, public, puffer, puppet, pursuer, pursuivant,
   rationalist, realist, remora, retainer, rooter, satellite, sectary,
   secular humanist, sensationalist, sensist, servant, shadow,
   skeptic, sticker, stooge, substantialist, successor, supporter,
   sycophant, syncretist, syrup, tagtail, tail, theist, thorn, thug,
   tout, touter, trainbearer, transcendentalist, upholder,
   utilitarian, vitalist, voluntarist, votary, ward heeler, zetetic



The Devil's Dictionary (1881-1906):

ADHERENT, n.  A follower who has not yet obtained all that he expects
to get.