The Collaborative International Dictionary of English v.0.48:

Enlighten \En*light"en\, v. t. [Pref. en- + lighten: cf. AS.
   inl[imac]htan. Cf. Enlight.]
   1. To supply with light; to illuminate; as, the sun
      enlightens the earth.
      [1913 Webster]

            His lightnings enlightened the world. --Ps. xcvii.
                                                  4.
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   2. To make clear to the intellect or conscience; to shed the
      light of truth and knowledge upon; to furnish with
      increase of knowledge; to instruct; as, to enlighten the
      mind or understanding.
      [1913 Webster]

            The conscience enlightened by the Word and Spirit of
            God.                                  --Trench.
      [1913 Webster]

WordNet (r) 3.0 (2006):

enlighten
    v 1: make understand; "Can you enlighten me--I don't understand
         this proposal" [syn: enlighten, edify]
    2: give spiritual insight to; in religion [syn: enlighten,
       irradiate]
    3: make free from confusion or ambiguity; make clear; "Could you
       clarify these remarks?"; "Clear up the question of who is at
       fault" [syn: clear, clear up, shed light on,
       crystallize, crystallise, crystalize, crystalise,
       straighten out, sort out, enlighten, illuminate,
       elucidate]