Adjective

(en adjective)

Pertaining to the foundation or basis; serving for the foundation. Hence: Essential, as an element, principle, or law; important; original; elementary.

* {{quote-magazine, date=2013-06-28, author=(Joris Luyendijk)

, volume=189, issue=3, page=21, magazine=(The Guardian Weekly) , title= Our banks are out of control , passage=Seeing the British establishment struggle with the financial sector is like watching an alcoholic […].  Until 2008 there was denial over what finance had become. […]  But the scandals kept coming, […]. A broad section of the political class now recognises the need for change but remains unable to see the necessity of a fundamental overhaul. Instead it offers fixes and patches.}}

Adjective

(en adjective)

Necessary.

Very important; of high importance.

* {{quote-magazine, date=2013-05-17

, author=George Monbiot, authorlink=George Monbiot , title=Money just makes the rich suffer , volume=188, issue=23, page=19 , magazine=(The Guardian Weekly) citation , passage=In order to grant the rich these pleasures, the social contract is reconfigured. The welfare state is dismantled. Essential public services are cut so that the rich may pay less tax. […]}}

Being in the basic form; showing its essence.

Don’t mind him being grumpy. That’s the essential Fred.

Really existing; existent.

* Webster (1623)

Is it true, that thou art but a name, / And no essential thing?

Such that each complementary region is irreducible, the boundary of each complementary region is incompressible by disks and monogons in the complementary region, and no leaf is a sphere or a torus bounding a solid torus in the manifold.

(medicine) Idiopathic.