6-Down, For One, is an ADDITIVE, SALT. An ADDITIVE is a substance added to something else to improve or preserve it. SALT is a common ADDITIVE used in food preparation and preservation. Other solutions for 6-Down, For One, include CARAVEL, a type of sailing ship used by the Portuguese and Spanish during the Age of Exploration; SCOT, a term used to refer to someone from Scotland; OXIDE, a chemical compound made up of oxygen and another element; SPY, a person employed to secretly observe and report on the activities of others; and petname, an affectionate name given to a pet or loved one.