tenebrific
Producing darkness, obscuring; (loosely) gloomy.
Tenebrific stars were once thought to be the source of darkness during the night.
Where it comes from
From New Latin tenebrificus, from Latin tenebrae (“darkness”) + -i- + -ficus (“making, causing”).
Adapted from the Wiktionary entry tenebrific (CC BY-SA 4.0).