"diagonal" - key terms from Wikipedia

above the diagonal
below the main diagonal
column and diagonal
cross the diagonal
diagonal
diagonal	argument
diagonal	avenue
diagonal	board
diagonal	cross
diagonal	elements
diagonal	entries
diagonal	form
diagonal	functor
diagonal	knee
diagonal	line
diagonal	mar
diagonal	matrices
diagonal	matrix
diagonal	measurement
diagonal	mirror
diagonal	orientation
diagonal	pair
diagonal	rib
diagonal	ribs
diagonal	row
diagonal	slash
diagonal	stripes
first diagonal
if the diagonal
main diagonal
strictly positive diagonal	entries