The Collaborative International Dictionary of English v.0.48:

Naturalistic \Nat`u*ral*is"tic\, a.
   1. Belonging to the doctrines of naturalism.
      [1913 Webster]

   2. Closely resembling nature; realistic. "Naturalistic bit of
      pantomime." --W. D. Howells.
      [1913 Webster]

WordNet (r) 3.0 (2006):

naturalistic
    adj 1: representing what is real; not abstract or ideal;
           "realistic portraiture"; "a realistic novel"; "in
           naturalistic colors"; "the school of naturalistic
           writers" [syn: naturalistic, realistic]

Moby Thesaurus II by Grady Ward, 1.0:

142 Moby Thesaurus words for "naturalistic":
   Cyrenaic, Eleatic, Epicurean, Marxian, Marxist, Megarian, Stoic,
   animist, animistic, atomistic, authentic, bona fide, candid,
   card-carrying, characteristic, commonsense, cosmotheistic,
   delineative, depictive, descriptive, dinkum, distinctive,
   distinguishing, eclectic, empirical, eudaemonistic, exemplary,
   existential, expositive, expressive, faithful,
   following the letter, general, genuine, good, graphic, hedonic,
   hedonist, hedonistic, honest, honest-to-God, humanist, humanistic,
   hylomorphous, hylotheistic, idealistic, inartificial,
   instrumentalist, lawful, legitimate, lifelike, literal,
   materialist, materialistic, mechanist, mechanistic, metaphysical,
   monistic, natural, naturalist, naturistic, nominalist, normal,
   orderly, original, panlogistical, pantheistic, positivist,
   positivistic, pragmatic, pragmatist, pure, quintessential,
   rationalistic, real, realist, realistic, regular, representative,
   rightful, sample, scholastic, sensationalistic, simon-pure, simple,
   sincere, sterling, sure-enough, syncretistic, theistic,
   transcendentalist, transcendentalistic, true to form, true to life,
   true to nature, true to reality, true to type, typal, typic,
   typical, unadulterated, unaffected, unassumed, unassuming,
   uncolored, unconcocted, uncopied, uncounterfeited, undisguised,
   undisguising, undistorted, unexaggerated, unexceptional,
   unfabricated, unfanciful, unfeigned, unfeigning, unfictitious,
   unflattering, unimagined, unimitated, uninvented, unpretended,
   unpretending, unqualified, unromantic, unsimulated, unspecious,
   unsynthetic, unvarnished, usual, utilitarian, verbal, verbatim,
   veridical, verisimilar, vitalistic, vivid, voluntarist,
   voluntaristic, well-drawn, word-for-word