1. very dark; gloomy: deep, Cimmerian caverns.
2. Classical Mythology. of, relating to, or suggestive of a western people believed to dwell in perpetual darkness.
The sunny English noon had swallowed him as completely as if he had gone out into Cimmerian night.
Edith Wharton, "Afterward," Tales of Men and Ghosts, 1910
... the darkness had become inky. Only the light from cabin windows which lay on the wet deck like shafts of silver relieved that Cimmerian effect.
Frederic S. Isham, A Man and His Money, 1912
In the Odyssey, the mythical Cimmerians lived at the edge of Oceanus that surrounds the earth in a city wrapped in mist and fog, where the sun never shines, near the entrance to Hades.
The historical, “real” Cimmerians are mentioned in Assyrian sources (Gimirri), the Hebrew Bible (Gomer in Genesis 10:2), and by the Greek historian Herodotus (5th century b.c.).
Herodotus says that the Cimmerians were nomads driven south from the steppes of southern Russia by the Scythians through the Caucasus Mountains, turned west, and c676 b.c. overthrew the kingdom of Phrygia (in west central Turkey), whose last king was Midas.
The connection between myth and history is that there are variant readings for Homer’s Kimmérioi—Cheimérioi, “Wintry People, Stormy people”; and Kerbérioi “Cerberus’s People,” both of which were displaced by the historical Cimmerians.
Cimmerian entered English in the 16th century in reference to the nomads, and in the 19th century in reference to the Homeric people.
(Source: dictionary.com word of the day)