heptadiagonal
Having nonzero entries along the main diagonal, the three diagonals on either side of…Having nonzero entries along the main diagonal, the three diagonals on either side of the main diagonal, and the three diagonals near each corner, only.
Dictionary text adapted from Wiktionary (Wiktionary contributors, CC BY-SA 4.0) and Open English WordNet / Princeton WordNet (CC BY 4.0, WordNet License); shared under CC BY-SA 4.0. Example sentences and recordings are credited where they appear.