essence late 14c., essencia (respelled late 15c. on French model), from L. essentia "being, essence," abstract noun formed in imitation of Gk. ousia "being, essence" (from on, gen. ontos, prp. of einai "to be"), from essent-, prp. stem of esse "to be," from PIE *es- (cf. Skt. asmi, Hittite eimi, O.C.S. jesmi, Lith. esmi, Goth. imi, O.E. 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.