Jet and Stygian

Jet adjective - Of the blackest black; similar to the color of jet or coal.

Stygian and jet are semantically related In some cases you can use "Stygian" instead an adjective "Jet".

Stygian adjective - Being without light or without much light.

Jet and stygian are semantically related in black topic. Sometimes you can use "Jet" instead an adjective "Stygian", if it concerns topics such as dark.