Source : Webster's Revised Unabridged Dictionary (1913)

Diagram \Di"a*gram\, n. [Gr. ?, fr. ? to mark out by lines; dia`
   through + ? to draw, write: cf. F. diagramme. See {Graphic}.]
   1. (Geom.) A figure or drawing made to illustrate a
      statement, or facilitate a demonstration; a plan.

   2. Any simple drawing made for mathematical or scientific
      purposes, or to assist a verbal explanation which refers
      to it; a mechanical drawing, as distinguished from an
      artistical one.

   {Indicator diagram}. (Steam Engine) See {Indicator card},
      under {indicator}