Adjective

(en adjective)

Obligatory; required or commanded by authority.

Attendance at a school is usually mandatory .

* 1999 , Ian Stewart, Jack Cohen, Figments of Reality: The Evolution of the Curious Mind , page 276

This kind of immediate control structure we take to be characteristic of the tribe, and it leads to a rather rigid type of system in which 'every action not mandatory is forbidden'.

Of, being or relating to a mandate.

Mandatory Palestine

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.