Source : Webster's Revised Unabridged Dictionary (1913)

Opaque \O*paque"\, a. [F., fr. L. opacus. Cf. {Opacous}.]
   1. Impervious to the rays of light; not transparent; as, an
      opaque substance.

   2. Obscure; not clear; unintelligible. [Colloq.]

Opaque \O*paque"\, n.
   That which is opaque; opacity. --Young.

Source : WordNet®

opaque
     adj 1: not clear; not transmitting or reflecting light or radiant
            energy; "opaque windows of the jail"; "opaque to
            X-rays" [ant: {clear}]
     2: not clearly understood or expressed [syn: {unintelligible}]