phlogiston

1. (chemistry, historical) The hypothetical fiery principle formerly assumed to be a necessary constituent of combustible bodies and to be given up by them in burning.Examples: "[…] air was universally reputed to be a simple or elementary body. It was liable, according to the phlogistians, to vitiation, by the addition to it of phlogiston[…] being more or less phlogisticated, according to the degree of its power to support respiration and combustion."; "Stahl argued that phlogiston could explain combustion, a central concern of eighteenth-century chemistry."historicaluncountableusually