opaque

Etymology

From Middle English opake, from Latin opacus (“shaded, shady, dark”) (of unknown origin), later reinforced from Middle French opaque. Doublet of ubac.

adj

1. Neither reflecting nor emitting light.
   We have agreed that heat is energy to begin with. Light is also a form of energy for when absorbed by any opaque substance it turns completely into heat. 1968, Isaac Asimov, Photosynthesis, Basic Books, Inc., page 60
2. Allowing little light to pass through, not translucent or transparent.
3. (figurative) Unclear, unintelligible, hard to get or explain the meaning of.
4. (figurative) Obtuse, stupid.
5. (computing) Describes a type for which higher-level callers have no knowledge of data values or their representations; all operations are carried out by the type's defined abstract operators.

noun

1. (obsolete, poetic) An area of darkness; a place or region with no light.
   Through this opaque of Nature and of Soul, / This double night, transmit one pitying ray, / To lighten, and to cheer. 1745, Edward Young, Night-Thoughts, section I
2. Something which is opaque rather than translucent.

verb

1. (transitive) To make, render (more) opaque.