Question: What is the etymology of the word *ketchup*? I've tried searching on Google without a definitive answer.

Answer: 
This is undocumented, but I heard that the term 'ketchup' originated with spice traders who travelled in Southeast Asia/ Hong Kong/ Canton province. In Cantonese, the term 'chup' means literally 'sauce'. In the provincial areas of Canton, tomatoes are called "Fan Ke". In a slang phrase, Ke-Chup or Ket-Chup means tomato sauce.
Ketchup 果子汁is a Taiwanese word that means fruit juice. The name was brought back to Europe by the Dutch in the early 17th Century when Taiwan was a Dutch colony. 

Along with ketchup, tea was brought back to Europe, the word "tea" came from Taiwanese.

* Taiwanese *te*
* Dutch *thee*
* German *tee*
* French *the*
* Spanish *te*
* English *tea*