As an adjective:
* Opaque means not able to be seen through; not transparent.
* Example: "The window was opaque, covered in dust."
As a noun:
* Opaque refers to something that is opaque, especially a material that does not allow light to pass through.
* Example: "The artist used an opaque to create depth in the painting."
The most common usage is as an adjective, describing something that is not transparent.