essential

Adjective

• defining rights and duties as opposed to giving the rules by which rights and duties are established
  • substantive law
    

• being or relating to or containing the essence of a plant etc
  • essential oil
    

• of the greatest importance
  • the all-important subject of disarmament
    
  • crucial information
    
  • in chess cool nerves are of the essence
    

• basic and fundamental
  • the essential feature
    

• absolutely necessary; vitally necessary
  • essential tools and materials
    
  • funds essential to the completion of the project
    
  • an indispensable worker
    

Noun

• anything indispensable
  • food and shelter are necessities of life
    
  • the essentials of the good life
    
  • allow farmers to buy their requirements under favorable conditions
    
  • a place where the requisites of water fuel and fodder can be obtained
    

Related words

• Synonyms: 
  substantive , all-important(a) , all important(p) , crucial , of the essence(p) , indispensable , necessity , requirement , requisite , necessary
• Antonyms: 
  adjective , procedural , inessential , unessential , nonessential