1.anything indispensable;
food and shelter are necessities of life
2.absolutely necessary; vitally necessary;
essential tools and materials
3.basic and fundamental;
the essential feature
4.of the greatest importance;
the all-important subject of disarmament
5.being or relating to or containing the essence of a plant etc;
essential oil
6.applying to essential legal principles and rules of right;
substantive law
7.absolutely required and not to be used up or sacrificed