Related Clues:

• A question in work (English) is obscure
• Impenetrable composition leading to audience's discomfort
• Low went up
• Dense crop — a question of where to look
• Profound - cunning - sea - bass
• Profound - sea
• Non-transparent
• Wise - difficult to understand
• Without lustre
• Difficult to comprehend
• Puzzling - dull
• Far down
• Impervious to light — hard to understand
• Like a bass voice
• Many-layered