necessary

Adjective

• unavoidably determined by prior circumstances
  • the necessary consequences of one's actions
    

• absolutely essential

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: 
  necessity , essential , requirement , requisite
• Antonyms: 
  unnecessary , unneeded , inessential , nonessential