Is it ensure, insure, or assure?
1878, shortening of graphic formula (see graphic). The verb meaning "charted on a graph" is from 1889. Related: Graphed; graphing.
word-forming element meaning "instrument for recording; something written," from Greek graphe "writing," from graphein "to write, express by written characters," earlier "to draw, represent by lines drawn" (see -graphy).
An instrument for writing, drawing, or recording: cardiograph.