Английский Этимологический словарь - diagram (n.)

- 1619, from Fr. diagramme, from L. diagramma, from Gk. diagramma (gen. diagrammatos) "that which is marked out by lines," from diagraphein "mark out by lines, delineate," from dia- "across, out" + graphein "write, mark, draw." The verb is 1840, from the noun.