'phlogistic' originates from New Latin, specifically the word 'phlogisticus', ultimately formed from 'phlogiston' (Modern Latin), which itself comes from Greek roots related to fire (see below).

'phlogisticus' in New Latin was formed from 'phlogiston' (Modern Latin), 'phlogiston' was borrowed from Greek phlogistos / phlogizein (from phlox/φλόξ 'flame' or the root meaning 'to burn'), and the adjective entered English usage in the 18th century alongside discussions of the phlogiston theory.

Initially it meant 'pertaining to phlogiston or the phlogiston theory'; over time, as the theory became obsolete, the term grew rare and is now chiefly of historical or metaphorical interest, with occasional archaic uses meaning 'combustible' or 'promoting inflammation/heat'.