basis

Noun

• the most important or necessary part of something
  • the basis of this drink is orange juice
    

• the fundamental assumptions from which something is begun or developed or calculated or explained
  • the whole argument rested on a basis of conjecture
    

• a relation that provides the foundation for something
  • they were on a friendly footing
    
  • he worked on an interim basis
    

Related words

• Synonyms: 
  base , foundation , fundament , groundwork , cornerstone , footing , ground