The word "catsup" is correct and can be used in written English.
You can use it to refer to a type of sauce made from tomatoes that is typically used on hamburgers and hot dogs. For example, "I like to put catsup on my burgers for added flavor."
By 1905 it had become the H.J. Heinz Company, the largest producer of pickles, vinegar, and ketchup (catsup) in the United States.
Romney Top Chef — Ann impresses the judges with Mitt's favorite meal of meatloaf cakes with catsup and brown sugar.
"I would write ads for deodorants or labels for catsup bottles, if I had to," he told The Paris Review in 1967.
John H. Worsham of the Stonewall Brigade wrote of "vast storehouses filled with everything to eat, and sutler's stores filled with all the delicacies, potted ham, lobster, tongue, candy, cakes, nuts, oranges, lemons, pickles, catsup, mustard, etc".
"Ketchup" has gradually taken over from "catsup," a British spelling.
Mr. Smith and the chef, Daniel Mowles, tried for balance between North and South, so there was fried catfish with "Confederate catsup" to offset the rabbit, which was served with "Boston mustard".
The epitome of the miserly millionaire, Burns is a caricature of corporate America with a taste for catsup, a history of Nazi sympathising and a wardrobe that would send PETA into meltdown.
I could not manage to serve forth to Mark Twain the "Sheep-head and croakers, from New Orleans," or the "Prairie hens, from Illinois," that he dreamed of in European boarding houses ninety years ago, but mashed potatoes with catsup are ready to hand when he says the word.
When my turn came, I said, "Mashed potatoes and catsup".
