The Collaborative International Dictionary of English v.0.48:

enlightening \enlightening\ adj.
   1. enlightening so as to encourage intellectual or moral
      improvement.

   Syn: edifying.
        [WordNet 1.5]

   2. tending to increase knowledge or dissipate ignorance; as,
      an enlightening glimpse of government in action.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

enlightening
    adj 1: tending to increase knowledge or dissipate ignorance; "an
           enlightening glimpse of government in action"; "an
           illuminating lecture" [syn: enlightening,
           informative, illuminating] [ant: unenlightening,
           unilluminating]
    2: enlightening or uplifting so as to encourage intellectual or
       moral improvement; "the paintings in the church served an
       edifying purpose even for those who could not read" [syn:
       edifying, enlightening] [ant: unedifying,
       unenlightening]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "enlightening":
   advisory, allegorizing, annotative, autodidactic, brightening,
   broadening, clarifying, coeducational, communicative, critical,
   cultural, demonstrative, demythologizing, didactic, disabusing,
   disciplinary, disenchanting, disillusionary, disillusioning,
   disillusive, edifying, editorial, educating, educational,
   educative, elucidative, euhemeristic, exegetic, exemplificative,
   exhortatory, explaining, explanatory, explicative, explicatory,
   expositive, expository, glossarial, homiletic, hortatory,
   illuminant, illuminating, illuminative, illumining, illustrative,
   informational, informative, informing, initiatory, instructive,
   introductory, lecturing, lightening, lighting, monitory, preaching,
   preceptive, propaedeutic, rationalistic, rationalizing,
   scholiastic, self-teaching, teaching, tuitionary, undeceiving