phlogiston

From Wiktionary

Noun[change]

Singular
phlogiston

Plural
none

  1. (historical) An ancient Greek idea of energy, which was used up when things burned. For example, burning wood would use up the phlogiston in the wood and the air (which actually had no oxygen). When the air or the wood had lost their phlogiston they could not be used. Scientists now know this idea is wrong.