An opaque envelope is an envelope that is transparent or translucent. It is dull in color and does not allow light to pass through.
Aluminum foil is opaque.
Opaque
Yes, a carpet is opaque.
Opaque
There are many objects that no light can pass through, although of course, it depends on what type of light you're talking about. The name of the type of object that visible light cannot pass through is called opaque.