diagram (n.)

1610s, "an illustrative figure giving only the outlines or general scheme of the object;" 1640s in geometry, "a drawing for the purpose of demonstrating the properties of a figure;" from French diagramme, from Latin diagramma "a scale, a musical scale," from Greek diagramma "geometric figure, that which is marked out by lines," from diagraphein "mark out by lines, delineate," from dia "across, through" (see dia-) + graphein "write, mark, draw" (see -graphy). Related: Diagrammatic; diagrammatically.

The verb, "to draw or put in the form of a diagram," is by 1822, from the noun. Related: Diagrammed; diagramming.

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Definitions of diagram from WordNet
diagram (v.)
make a schematic or technical drawing of that shows interactions among variables or how something is constructed;
Synonyms: plot
diagram (n.)
a drawing intended to explain how something works; a drawing showing the relation between the parts;