Lacking transparency? (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
opaque
'lacking transparency?' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for opaque that I've seen before include "Not transparent, light can't pass through" , "Hazy, unclear" , "Not translucent" , "Hard to understand, see through" , "Dark" .)