On his second expedition to the Caribbean, Captain John Hawkins did some sailing around the coasts of Venezuela and Mexico. When he returned to England, he brought back with him a shark, and, by extension, the word for it. Where this comes from was never elaborated by his crew, but there are several theory. The most possible, and, indeed, most interesting one, is that shark comes from the ancient Mayan Yacatec word xoc, which would make it the only English borrowing from that language. This could have been picked up off the shores of the Yucatan following a particularly nasty naval battle with the Spaniards which ended up in several people getting gobbled up by sharks. Other possibilities include a Germanic word, like Dutch schrock, meaning "glutton" or German schurke, meaning "scoundrel". None of these are confirmed and all are mere possibilities. You could say we're just testing the waters.
Adam Aleksic, a freshman studying linguistics at Harvard University, has been described as the internet's sixth most famous etymologist. He has disturbing interests in words, vexillology, geography, board games, limericks, and law, and he loves writing about himself in the third person.
The Etymology Nerd