The Collaborative International Dictionary of English v.0.48:

Illustrative \Il*lus"tra*tive\, a.
   1. Tending or designed to illustrate, exemplify, or
      elucidate.
      [1913 Webster]

   2. Making illustrious. [Obs.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

illustrative
    adj 1: clarifying by use of examples [syn: exemplifying,
           illustrative]
    2: serving to demonstrate [syn: demonstrative, illustrative]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "illustrative":
   allegorizing, annotative, apish, clarifying, critical, delineatory,
   demonstrative, demythologizing, depictive, echoic, editorial,
   elucidative, embodying, enlightening, euhemeristic, exegetic,
   exemplificative, explaining, explanatory, explicative, explicatory,
   expositive, expository, figurative, glossarial, graphic,
   ideographic, illuminating, illuminative, illustrational, imitative,
   incarnating, limning, mimetic, mimish, onomatopoeic, personifying,
   pictographic, pictorial, portraying, rationalistic, rationalizing,
   representational, representative, representing, scholiastic,
   simulative, symbolizing, typifying, vivid