Shark
late Middle English: of unknown origin.
wiktionary
From Middle English shark (used by Thomas Beckington in 1442 to refer to a kind of fish), [1] of uncertain origin. Most likely from a semantic extension of the German-derived shark(“scoundrel”), see below. The fish was originally called a dogfish or haye in English and Middle English.
From German Schurke(“scoundrel”); compare Dutch schurk.
Probably from the "steal" senses above, but perhaps related to shear. Compare shirk.
etymonline
shark (n.)
by 1560s, perhaps mid-15c., if an isolated instance in a diary in Middle English Compendium is the same word, of uncertain origin.
The meaning "dishonest person who preys on others," though attested from 1599 (sharker "artful swindler" in this sense is from 1594), may be the original sense, later transferred to the large, voracious marine fish. If so, it is possibly from German Schorck, a variant of Schurke "scoundrel, villain," agent noun of Middle High German schürgen (German schüren) "to poke, stir."
On an old theory, the English word is from a Mayan word, xoc, which might have meant "shark." Northern Europeans seem not to have been familiar with the larger sort of sharks before voyages to the tropics began. A slightly earlier name for it in English was tiburon, from Spanish tiburón (1520s), which probably is from a native word from South America, such as Tupi uperu "shark" (source also of Portuguese tubarão, Catalan tauró).
Middle English had hound-fish (early 14c.), which probably was used of dogfish and other small sharks. The general Germanic word seems to be represented by Old Norse har (Norwegian hai, Danis haj, Dutch haai, German Hai, also borrowed in Finnish, Latvian), which is of unknown origin. French requin is literally "grimacer," from Norman requin, from Old French reschignier "to bare the teeth, grimace." An ancient Greek word for a shark was karkharias, from karkharos "sharp, jagged, biting." Latin used squalus, from the root of English whale (n.); Lithuanian ryklys is literally "swallower."
The English word was applied (or re-applied) to voracious or predatory persons, on the image of the fish, from 1707 (originally of pick-pockets); loan shark is attested from 1905. Sharkskin (1851) was used for binding books, etc. As the name of a type of fabric held to resemble it, it is recorded from 1932.
There is the ordinary Brown Shark, or sea attorney, so called by sailors; a grasping, rapacious varlet, that in spite of the hard knocks received from it, often snapped viciously at our steering oar. [Herman Melville, "Mardi"]
shark (v.)
c. 1600, "to live by one's wits," of uncertain origin (see shark (n.)); according to OED, at least partly a variant of shirk. Meaning "obtain by sharking" is from 1610s. Related: Sharked; sharking.
