* Jan Baptista van Helmont (1579-1644), a Flemish chemist, first used the term "gas" in his book "Ortus Medicinae" (published posthumously in 1648).
* He derived the word from the Greek word "chaos", which refers to the formless void that existed before creation.
* Helmont used "gas" to describe a substance he observed while experimenting with charcoal. He noticed that when charcoal was burned, it released an invisible vapor that was distinct from air. He named this vapor "gas" because it was a disordered, chaotic substance.
* It's important to note that Helmont's understanding of "gas" was different from our modern definition. He believed it was a single, universal substance with various properties, rather than a collection of different chemical compounds.
Over time, the word "gas" came to be used more broadly to refer to any substance that exists in a state of matter that is neither solid nor liquid. This modern definition is now widely accepted.