Just before we were to board, the kids, as is their wont, got hungry, so I made a quick dash to a nearby hot dog stand. At the stand were some British tourists, discussing what to put on their weenie in a bun.
Wife [to husband]: Do you want mustard or sauce?
Wife [to vendor]: Two hot dogs, please. One with mustard and one with timahtoe.
See what happened there? Among(st) themselves, they speak of "sauce." Then, to translate the term to American English, they use "timahtoe," their variant of tomato.
Never in the whole exchange did "ketchup" or "catsup" enter the discussion. The vendor was obviously seasoned and took it in stride, giving them both "sauce."