ketchup (n.) Look up ketchup at Dictionary.com
1711, said to be from Malay kichap, but probably not original to Malay. It might have come from Chinese koechiap "brine of fish," which, if authentic, perhaps is from the Chinese community in northern Vietnam [Terrien de Lacouperie, in "Babylonian and Oriental Record," 1889, 1890]. Catsup (earlier catchup, 1680s) is a failed attempt at Englishing, still in use in U.S., influenced by cat and sup.

Originally a fish sauce, the word came to be used in English for a wide variety of spiced gravies and sauces; "Apicius Redivivus; or, the Cook's Oracle," by William Kitchiner, London, 1817, devotes 7 pages to recipes for different types of catsup (his book has 1 spelling of ketchup, 72 of catsup), including walnut, mushroom, oyster, cockle and mussel, tomata, white (vinegar and anchovies figure in it), cucumber, and pudding catsup. Chambers's Encyclopaedia (1870) lists mushroom, walnut, and tomato ketchup as "the three most esteemed kinds." Tomato ketchup emerged c.1800 in U.S. and predominated from early 20c.