noun: the part of a ship that is above the main deck
noun: the part of a building that is above its foundations (the parts below ground)
noun: an idea or social system that has developed from a more basic idea or system

Hughes
ALTHOUGH I am confident that the foundation on which I have been building is firm, and will never fail, I also feel that there are probably errors in raising the superstructure. "Truthful deductions must ultimately harmonise; like light, they will shine by their own effulgence." "If, however, we determine that we will not receive any truth against which objections can be raised, we shall remain in a state of universal scepticism, for against truths of every description objections have been and may be suggested." Appearances are often contrary to facts— "the straight stick looks crooked in the tide." And the question has always to be decided, whether the objections neutralise the positive evidences in favour of the truth of any assertion. [Harmonies of Tones and Colours, General Remarks on Harmonies of Tones and Colours, page 12]