Opacity
Opaque
noun, な adjective
You know that 透明 is "transparency" or "transparent" - so, if something is not transparent, then it is opaque, making this word opacity.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
不透明な窓がある女子の更衣室です。
This is the girls locker room, which has opaque windows.