phlogistian adjective 1noun 1forms 1 adjective1 •Of or pertaining to phlogiston or phlogiston theory.In Davy's time it was still necessary in considering any novel fact to keep the phlogistian hypothesis in view, and to demonstrate its inability to explain the new discoveries. — 1894 noun1 •A believer in the existence of phlogiston.It [air] was liable, according to the phlogistians, to vitiation, by the addition to it of phlogiston, […] — 1810 formsphlogistians
