noun (n)

• the fundamental assumptions from which something is begun or developed or calculated or explained(noun.cognition)

  Synonym:
  base, basis, cornerstone, foundation, fundament
  

  source: wordnet30
• lowest support of a structure(noun.artifact)

  Synonym:
  base, foot, foundation, fundament, substructure, understructure
  

  source: wordnet30
• preliminary preparation as a basis or foundation(noun.act)

  Example:
  We are prepared today because of groundwork that was done ten years ago.
  

  source: wordnet30
• That which forms the foundation or support of anything; the basis; the essential or fundamental part; first principle.(noun)

  source: webster1913