noun
: a theory in 18th century chemistry disproved by Lavoisier: every combustible substance is a compound of phlogiston and the phenomena of combustion are due to the liberation of phlogiston with the other constituent left as a residue
the phlogiston theory thus provided a general explanation of the chemical processes of oxidation and reduction: oxidation was taken to be the liberation of phlogiston, and reduction combination with phlogiston — Linus Pauling