'Ketchup' started out as a fermented fish sauce with no tomatoes anywhere near it

The word likely traces to 'kê-tsiap', a fermented fish brine sauce in Hokkien Chinese trading ports, picked up by British sailors in Southeast Asia. English cooks spent over a century experimenting with mushroom, walnut and oyster versions before Americans added tomatoes and sugar sometime in the early 1800s, creating the ketchup sold today.

— Wikipedia contributors, Ketchup — Etymology and history section