Brimstone is an old-fashioned word for sulfur, a yellow chemical element that burns with a distinctive blue flame and produces a strong, unpleasant smell like rotten eggs. You might encounter brimstone in old books or religious texts, where it often appears paired with fire in the phrase fire and brimstone, describing divine punishment or destruction.

Sulfur catches fire easily and was one of the few minerals ancient people could burn. Volcanoes release sulfur, creating that characteristic rotten-egg smell, which is why volcanic areas were sometimes described as smelling of brimstone.

In nature, you can find sulfur in volcanic regions, hot springs, and certain minerals. Scientists use sulfur today in everything from matches and fireworks to fertilizers and rubber tires. While we rarely call it brimstone anymore, the old word survives in literature and historical writings, reminding us of a time when people named things based on what they did rather than on their chemical properties.