@hue-man,
I think etymology is useful. Others might not. For me the linguistic turn in philosophy was crucial. Most abstractions are dead/literalized/context-learned metaphors. I think we should look at our tools, decide if we know what we are about.
essence late 14c., from L. essentia "being, essence," abstract n. formed in imitation of Gk. ousia "being, essence" (from on, gen. ontos, prp. of einai "to be"), from 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 (mid-14c.).
existence late 14c., from O.Fr. existence, from L.L. existentem "existent," prp. of L. existere "stand forth, appear," and, as a secondary meaning, "exist;" from ex- "forth" + sistere "cause to stand" (see
assist).