essential essential /iːˈsɛnʃəl/

adjective

1. () Absolutely necessary; vitally necessary  ( indispensable , essential )
   absolutely necessary; vitally necessary
    Essential tools and materials
   essential tools and materials
    Funds essential to the completion of the project
   funds essential to the completion of the project
    An indispensable worker
   an indispensable worker
   
2. () Basic and fundamental  ( essential )
   basic and fundamental
    The essential feature
   the essential feature
   
3. () Of the greatest importance  ( all important , crucial , of the essence , all-important , essential )
   of the greatest importance
    The all-important subject of disarmament
   the all-important subject of disarmament
    Crucial information
   crucial information
    In chess cool nerves are of the essence
   in chess cool nerves are of the essence
   
4. (law) defining rights and duties as opposed to giving the rules by which rights and duties are established  ( essential , substantive )
   (law) defining rights and duties as opposed to giving the rules by which rights and duties are established
    Substantive law
   substantive law
   
5. Being or relating to or containing the essence of a plant etc  ( essential )
   being or relating to or containing the essence of a plant etc
    Essential oil
   essential oil
   

noun

1. () Anything indispensable  ( necessary , requisite , essential , necessity , requirement )
   anything indispensable
    Food and shelter are necessities of life
   food and shelter are necessities of life
    The essentials of the good life
   the essentials of the good life
    Allow farmers to buy their requirements under favorable conditions
   allow farmers to buy their requirements under favorable conditions
    A place where the requisites of water fuel and fodder can be obtained
   a place where the requisites of water fuel and fodder can be obtained