Open English Wordnet
Nouns
(n)basis, base, foundation, fundament, groundwork, cornerstonethe fundamental assumptions from which something is begun or developed or calculated or explained“the whole argument rested on a basis of conjecture”
(n)foundation, base, fundament, foot, groundwork, substructure, understructurelowest support of a structure“it was built on a base of solid rock”, “he stood at the foot of the tower”
(n)groundworkpreliminary preparation as a basis or foundation“we are prepared today because of groundwork that was done ten years ago”