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1. A humorous name, term, or term of endearment for a fat, or slightly overweight, person.

2. A humorous name, or term, for a morbidly obese person, provided they don't hear you.
Woman: "Does my bum look big in this?"
Partner: "Of course it does Gigantopotamus"

From the words gigantic and hippopotamus.
See: Chunkosaurus
by Goatlips July 12, 2008
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