Oxygen
In one experiment, Lavoisier found that there was no increase in weight when tin and air were heated in a closed container. He also found that air rushed in when the container was opened. After this, he found that the weight of the tin had increased by the same amount as the weight of the air that rushed in. He published his findings in 1777.  He wrote that air was made up of two gases. One he called "vital air" (oxygen), which is needed for combustion and respiration. The other (nitrogen) he called "azote", which means "lifeless" in Greek. (This is still the name of nitrogen in some languages, including French.)