'Stygian,' 'Umbra,' and Other Words for Darkness Stygian. Definition: extremely dark, gloomy, or forbidding. ... Umbra. The Latin word for shade or shadow is umbra, a word that has spread its shadow over a wide range of words in English. ... Crepuscule. ... Tenebrous. ... Gloaming. ... Somber. ... Caliginous. ... Photophobic.