An example of diagonal is a line going from the bottom left corner of a square to the top right corner.
Origin of diagonal
- Latin diagōnālis from Greek diagōnios from angle to angle dia- dia- gōniā angle, corner genu-1 in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition
- From Middle French diagonal, from Latin diagōnālis, from Ancient Greek διαγώνιος (diagonios, “from angle to angle”), from διά (dia, “across”) + γωνία (gonia, “angle”).