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Two broad categories of absorbing boundary conditions (ABCs) are typically utilized in the finite-element method (FEM) for mesh truncation. The first class of hybrid techniques, which are global and rigorous in nature, cause the augmented FEM system matrix to exhibit a loss of sparsity. In the second class of ABCs, which are strictly local but approximate in character, the sparsity of the FEM system matrix is preserved at the expense of numerical accuracy. In this article we synthesize a novel wideband boundary condition based on an application of the reciprocity theorem. Although this boundary condition is essentially global in nature, it tends to maintain the sparsity of the FEM matrix to the same extent that the numerical ABCs (NABCs) do. [ABSTRACT FROM AUTHOR]