Related Clues:

• Tough to see through
• Opposite of ''transparent''
• Inside shop a queue's becoming dense
• Obscure old film on teeth student ignored
• Impervious to sight
• Impenetrable work leads to awkward questions, upsetting editor
• Ring Panama and Quebec as it's not clear
• Impenetrable to light
• Unclear over Press Association question's point
• Cloudy — obscure
• Obscure work -- a search with street cleared
• Initially old puzzles appear quite unusual, even cryptic
• Foggy — incomprehensible
• Unable to be seen through
• Work by area (western half of Quebec) that's dull