es·sence 
(ĕsəns)
(ĕsəns)n.
Idioms: 1.
a. The intrinsic or indispensable quality or qualities that serve to characterize or identify something: The essence of democracy is the freedom to choose.
b. Philosophy The inherent, unchanging nature of a thing or class of things, especially as contrasted with its existence.
2. The most important part or aspect of something: The essence of her argument is that the policy is wrongheaded.
3.
a. An extract that has the fundamental properties of a substance in concentrated form.
b. Such an extract in a solution of alcohol.
c. A perfume or scent.
4. One that has or shows an abundance of a quality as if highly concentrated: a neighbor who is the essence of hospitality.
5. Something that exists, especially a spiritual or incorporeal entity.
in essence
By nature; essentially: He is in essence a reclusive sort.
of the essence
Of the greatest importance; crucial: Time is of the essence.
[Middle English essencia and French essence, both from Latin essentia, from esse, to be, from the presumed present participle *essēns, *essent- (on the model of differentia, difference, from differēns, different-, present participle of differre, to differ), created to translate Greek ousiā (from ousa, feminine present participle of einai, to be) ; see es- in the Appendix of Indo-European roots.]