Is it ensure, insure, or assure?
late 14c., "candlestick with a screen," a shortening of Old French esconse "lantern, hiding place," from Medieval Latin sconsa, from Latin absconsa, fem. past participle of abscondere "to hide" (see abscond). Meaning "metal bracket-candlestick fastened to a wall" is recorded from mid-15c.
wooden or metal bracket affixed to a wall and designed to hold candles, lamps, or other types of illumination. One of the earliest forms of lighting fixtures for domestic and public use, sconces first appeared in Classical antiquity, but more elaborate variants were stimulated by the custom that arose in the European Middle Ages of affixing metal sconces holding candles to the walls of churches when they were consecrated. Various elaborations and refinements were added in the 17th century, including mirrors or metal reflectors to intensify the light.