opacous

From Latin opacus (“shaded, shady, dark”) +‎ -ous.

opacous (not comparable)

1. (obsolete, chiefly poetic) Not shining or illuminated; dark. [17th-20th c.]
   • 1667, John Milton, Paradise Lost:

     The firm opacous Globe / Of this round World, whose first convex divides / The luminous inferior Orbs.

2. (obsolete) Not allowing the passage of light; opaque. [17th-19th c.]
   • 1665, Robert Hooke, Micrographia, X:

     [I]f you take ammel that is almost opacous, and grind it very well on a Porphyry, or Serpentine, the small particles will by reason of their flaws, appear perfectly opacous […].

   • Grew

     The upper wings are opacous; at their hinder ends, where they lap over, transparent, like the wing of a fly.