'jet-black' originates from the word 'jet,' a type of lignite, which is a precursor to coal. The word 'jet' comes from the Old French 'jaiet,' which in turn comes from the Latin 'gagates,' referring to a black stone found near the town of Gagas in Asia Minor.

'jet' changed from the Old French word 'jaiet' and eventually became the modern English word 'jet.'

Initially, 'jet' referred to the black stone used in jewelry, but over time it evolved to describe the color itself, leading to the term 'jet-black.'