Ketchup and catsup are basically two different spellings for just one thing. There is a modern, a version that has been westernized, of seasoning or condiment, which some European traders were introduced to when they visited the Far East during the late 17th century. A matter of debate is what the condiment was and where it was found. The early western versions of the condiment were sometimes called ketchup.
A book was published in England in the year 1727, which included the recipes, calling for shallots, vinegar, cloves, ginger, white wine, mace, nutmeg, anchovies, pepper, and lemon peel. It was about a century later that tomatoes found its way into the sauce in a recipe in an American cookbook published in 1801. Later, another alternative spelling popped up, mentioned in a 1730 Jonathan Swift poem: "And, for our home-bred British cheer, Botargo [a fish roe-based relish], catsup, and career [caviar].