The Collaborative International Dictionary of English v.0.48:

Artifact \Ar"ti*fact\, n. [L. ars, artis, art + facere, factum,
   to make.]
   1. (Arch[ae]ol.) A product of human workmanship; -- applied
      esp. to the simpler products of aboriginal art as
      distinguished from natural objects.

   Syn: artefact.
        [Webster 1913 Suppl.]

   2. Any product of human workmanship; -- applied both to
      objects made for practical purposes as well as works of
      art. It is contrasted to natural object, i.e. anything
      produced by natural forces without the intervention of
      man.

   Syn: artefact.
        [PJC]

   3. (Biol.) A structure or appearance in protoplasm due to
      death, method of preparation of specimens, or the use of
      reagents, and not present during life.

   Syn: artefact.
        [Webster 1913 Suppl.]

   4. (Technology) an object, oservation, phenomenon, or result
      arising from hidden or unexpected causes extraneous to the
      subject of a study, and therefore spurious and having
      potential to lead one to an erroneous conclusion, or to
      invalidate the study. In experimental science, artifacts
      may arise due to inadvertant contamination of equipment,
      faulty experimental design or faulty analysis, or
      unexpected effects of agencies not known to affect the
      system under study.

   Syn: artefact.
        [PJC]

WordNet (r) 3.0 (2006):

artifact
    n 1: a man-made object taken as a whole [syn: artifact,
         artefact] [ant: natural object]

Moby Thesaurus II by Grady Ward, 1.0:

93 Moby Thesaurus words for "artifact":
   affair, ancient manuscript, antique, antiquity, archaism, article,
   brainchild, cave painting, child, coinage, composition, concoction,
   creation, creature, crowning achievement, dingus, distillation,
   dofunny, dohickey, dojigger, dojiggy, domajig, domajigger, doodad,
   dowhacky, effect, end product, eolith, eppes, essence, etwas,
   extract, flumadiddle, fossil, fruit, gadget, gigamaree, gimmick,
   gizmo, handiwork, hickey, hootenanny, hootmalalie, invention,
   issue, jigger, manufacture, masterpiece, masterwork,
   material thing, mezzolith, microlith, mintage, neolith,
   new mintage, object, offspring, opera, opus, opuscule, origination,
   outcome, outgrowth, paleolith, petrification, petrified forest,
   petrified wood, petroglyph, plateaulith, product, production,
   quelque chose, relic, reliquiae, remains, result, ruin, ruins,
   something, survival, thing, thingum, thingumabob, thingumadad,
   thingumadoodle, thingumajig, thingumajigger, thingumaree,
   thingummy, vestige, whatchy, widget, work