Source : Webster's Revised Unabridged Dictionary (1913)

Tenebrific \Ten`e*brif"ic\, a. [L. tenebrae darkness + facere to
   make.]
   Rendering dark or gloomy; tenebrous; gloomy.

         It lightens, it brightens, The tenebrific scene.
                                                  --Burns.

         Where light Lay fitful in a tenebrific time. --R.
                                                  Browning.

Source : WordNet®

tenebrific
     adj : dark and gloomy; "a tenebrous cave" [syn: {tenebrous}, {tenebrious}]