o·paque 
(ō-pāk)
(ō-pāk)adj.
1.
a. Impenetrable by light; neither transparent nor translucent.
b. Not reflecting light; having no luster: an opaque finish.
2. Impenetrable by a form of radiant energy other than visible light: a chemical solution opaque to x-rays.
3.
a. So obscure as to be unintelligible: "opaque, elusive, minimal meanings" (John Simon).
b. Mentally obtuse; dense.
n.
Something that is opaque, especially an opaque pigment used to darken parts of a photographic print or negative.
[Middle English opake, shady, and French opaque, opaque (from Old French, shady), both from Latin opācus.]
o·paquely adv.
o·paqueness n.