loan (n.)youdaoicibaDictYouDict[loan 词源字典]
mid-13c., from Old Norse lan, related to lja "to lend," from Proto-Germanic *laikhwniz (cognates: Old Frisian len "thing lent," Middle Dutch lene, Dutch leen "loan, fief," Old High German lehan, German Lehn "fief, feudal tenure"), originally "to let have, to leave (to someone)," from PIE *leikw- "to leave" (see relinquish).

The Norse word also is cognate with Old English læn "gift," which did not survive into Middle English, but its derived verb lænan is the source of lend. As a verb, loan is attested from 1540s, perhaps earlier, and formerly was current, but has now been supplanted in England by lend, though it survives in American English.

Loan word (1874) is a translation of German Lehnwort; loan-translation is attested 1933, from German Lehnübersetzung. Slang loan shark first attested 1900.[loan etymology, loan origin, 英语词源]
shark (n.)youdaoicibaDictYouDict
1560s, of uncertain origin; apparently the word and the first specimen were brought to London by Capt. John Hawkins's second expedition (landed 1565; see Hakluyt).
There is no proper name for it that I knowe, but that sertayne men of Captayne Haukinses doth call it a 'sharke' [handbill advertising an exhibition of the specimen, 1569]
The meaning "dishonest person who preys on others," though attested only 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."

But on another theory, the English word is from a Mayan word, xoc, which might have meant "shark." Northern Europeans seem not to have been familiar with sharks before voyages to the tropics began. A slightly earlier name for it in English was tiburon, via Spanish (where it is attested by 1520s), from the Carib name for the fish.

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"]