Unfathomable
Else clues• Cloudy
• Dense
• Hard to grasp
• Hard to understand
• Hardly transparent
• Impossible to see through
• Light-blocking
• Light-rejecting
• Muddy
• Not allowing light to pass through
• Not at all clear
• Not clear
• Not easily understood
• Not translucent
• Not transparent
• Not transparent or translucent
• Obscure or dark
• Opposite of transparent
• Thickheaded
• Unclear
• Without luster