I think “catsup” is the older spelling. I say “ketchup,” and that’s how it’s spelled everywhere I’ve lived (Northeast and Midwest US). When I see the word “catsup” it irritates me…because I want to pronounce it cat-sup, which sounds a little icky.
@DarkScribe I’ve never heard that before! Where do you live? “Tomato sauce,” where I live, is interchangeable with “marinara sauce” and “spaghetti sauce” and definitely doesn’t mean ketchup!