As black as coal; jet black; very black.(adjective)
Gnu Collaboartive International Dictionary of English: licensed under The Code Project Open License (CPOL)
Use "coal-black" in a sentence
"The most popular dance hall in the neighborhood was owned by Pete Williams, described as a “well-to-do, coal-black Negro, who has made an immense amount of money from the profits of his dance-house.”"
"Not a dozen feet away another Shetland, a coal-black one, was behaving as peculiarly as it was being treated."
"The moon was almost full, so there was plenty of light to steer by, although a coal-black cat nearly crossed my path, and I had a nasty swerve trying to avoid it."