The web site Word Detective has this to say about the word "jumbi":
According to the OED, "jumbi" (also spelled "jumby" and "jumbee," among other variations) is a West Indian word for "ghost" or "evil spirit," based on the African Kongo language word "zumbi," meaning charm or fetish. A very old copy of the Funk & Wagnalls Standard Dictionary of Folklore, Mythology and Legend (a marvelous two-volume set that I inherited from my father) adds that jumbies are usually the spirits of dead people that haunt the forests of Caribbean islands, and that the term may be related to the Haitian word "zombi," or what every horror-movie aficionado knows as "zombies."
Timothy is an elderly black sailor, probably the descendant of African slaves. The original religion of these slaves mixed with Catholicism when they were forced to convert, which resulted in what we call voodoo. Timothy may not practice voodoo, but he is superstitious and believes in voodoo curses. He believes that Stew Cat is an evil spirit, jumbi, that has taken the form of a cat.
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