1. A reference to not being clear; not transmitting radiant energy, sound, heat, etc.: Opaque elements are characterized by being opposite to that of transparency; for example, steel is an opaque material that blocks visible light.

Certain chemical solutions are opaque to ultraviolet radiations.

There was a dust cloud of opaque pollution over Karen's city that was caused by the dust storm.

2. Relating to something that is not clearly understood or expressed; not clear or lucid; obscure: Medical dictionaries too often provide the most opaque definitions of any of the other lexicons.

Despite the professor's help, the scientific presentation still seems opaque for some of his students.

3. Characteristic of impervious to light; not translucent or only slightly so: The winter opaque glass blocked any possibility of looking outside Adam's windows.
4. Descriptive of not allowing light to pass through: The opaque water of the muddy river made it impossible to see anything below the surface of the water.
5. Referring to not shining, without luster, not reflecting light; or being dark or dull: The opaque paint on Kate's car would not reflect the glare from the sun even on very sunny days.
6. Pertaining to dull, stupid, or unintelligent conversations: Some of the most opaque remarks are presented by certain radio talk-show hosts.

It's amazing how some politicians can pass such opaque bills that waste so much federal money.

7. Etymology: from opake which came from Latin opacus, "dark, shaded, shady" of uncertain origin. The current English spelling of opaque was influenced from about 1650 by French opaque which came from Latin.