1. Plan, project, design, scheme imply a formulated method of doing something. Plan refers to any method of thinking out acts and purposes beforehand: What are your plans for today? A project is a proposed or tentative plan, often elaborate or extensive: an irrigation project. Design suggests art, dexterity, or craft (sometimes evil and selfish) in the elaboration or execution of a plan, and often tends to emphasize the purpose in view: a misunderstanding brought about by design. A scheme is apt to be either a speculative, possibly impracticable, plan, or a selfish or dishonest one: a scheme to swindle someone.

Did you mean underpinning?