Is it ensure, insure, or assure?
mid-13c., "to draw, paint" (something), from Anglo-French purtraire, Old French portraire "to draw, to paint, portray" (12c.), literally "trace, draw forth," from por- "forth" (from Latin pro-; see pro-) + traire "trace, draw," from Latin trahere "to drag, draw" (see tract (n.1)). Meaning "depict in words, describe" is from late 14c. Related: Portrayed; portraying.