Blue jet and Jet-black

Blue jet noun - Atmospheric discharges (lasting 10 msec) bursting from the tops of giant storm clouds in blue cones that widen as they flash upward.

Jet-black and blue jet are semantically related. In some cases you can replace phrase "Jet-black" with "Blue jet", this phrases are similar.

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

Blue jet and jet-black are semantically related. You can use "Blue jet" instead a noun phrase "Jet-black".