Not allowing light to pass through; not transparent.

• Lacking translucence; visually impenetrable.

Difficult to understand; obscure or unclear.

• Hard to interpret or explain.

Computing: having a hidden representation; implementation concealed.

• Accessed only through its defined abstract operations.

Something opaque; a light-blocking substance or area.

• A region of darkness with no light.

To make or render opaque.

• To reduce transparency or clarity.