Essence began as a philosopher's invention. When Roman thinkers needed to translate Aristotle's Greek concept of ousia ('being, substance'), they derived essentia from the Latin verb esse ('to be'). The word entered English through Old French in the 14th century carrying heavy metaphysical baggage — it named the thing that makes something what it is, stripped of all accidents and appearances. Then the alchemists got hold of it. Medieval practitioners believed that distillation could extract the true 'essence' of a plant or mineral — its purest, most concentrated form. This practical sense gave us essential oils, vanilla essence, and the phrase 'in essence.' The alchemical thread stretches further than you might expect: in French, essence now means petrol, because refined fuel is a distilled extract. The word quintessence goes one step further, referring to the 'fifth essence' that medieval scholars believed pervaded the heavens beyond earth, water, air, and fire.