essence (n.)
late 14c., essencia (respelled late 15c. on French model), from Latin essentia "being, essence," abstract noun formed (in imitation of Greek ousia "being, essence") from essent-, present participle stem of esse "to be," from PIE *es- (cognates: Sanskrit asmi, Hittite eimi, Old Church Slavonic jesmi, Lithuanian esmi, Gothic imi, Old English eom "I am;" see be). Originally "substance of the Trinity," the general sense of "basic element of anything" is first recorded in English 1650s, though this is the base meaning of the first English use of essential.