A diamondoid, in the context of building materials for nanotechnology components, most generally refers to structures that resemble diamond in a broad sense: namely, strong, stiff structures containing dense, 3-D networks of covalent bonds.
You are likely aware of the beryllium acetate ensemble with a central oxide atom that can be considered diamondoid with interlocking six-membered Be2O3C rings. Although this is expanding the discussion rather than providing a focused answer, another area of recent interest and success is anchoring diamondoid lattices to gold or gold-nanocrystals with thiol linkers for multiple purposes and measurements.