tenebrific

• While old Traun is kept luminous as mid-day; the circumambient atmosphere of Pandours is tenebrific to —  History of Friedrich II of Prussia — Volume 15
• "Now" (says the sympathetic Other Half-Rome), "begins the tenebrific passage of the tale." —  Browning's Heroines
• Now begins "the tenebrific passage of the tale." —  Browning's Heroines
• The _cui bono_ of these doctrines may not, it is true, be expressible by arithmetical computations: the subject also is perplexed with obscurities, and probably with manifold delusions; and too often its interpreters with us have been like 'tenebrific stars,' that 'did ray out darkness' on a matter itself sufficiently dark. —  The Life of Friedrich Schiller Comprehending an Examination of His Works
• One Didymus is, moreover, related to have written six thousand books on the single subject of grammar, a topic rendered only more tenebrific by the labours of his successors, and which seems still to possess an attraction for authors in proportion as they can make nothing of it. —  The Biglow Papers

Roget's II: The New Thesaurus