"Shrove Tuesday, last day of carnival, day of eating and merrymaking before the fasting season of Lent," 1690s, French, literally "fat Tuesday," from mardi "Tuesday" (12c. in Old French, from Latin Martis diem "day of the planet Mars;" see Tuesday) + gras "fat," from Latin crassus, "thick," which is of unknown origin.
third day of the week, Old English tiwesdæg, from Tiwes, genitive of Tiw "Tiu," from Proto-Germanic *Tiwaz "god of the sky," the original supreme deity of ancient Germanic mythology, differentiated specifically as Tiu, ancient Germanic god of war, from PIE *deiwos "god," from root *dyeu- "to shine," in derivatives "sky, heaven, god." Cognate with Old Frisian tiesdei, Old Norse tysdagr, Swedish tisdag, Old High German ziestag.
The day name (second element dæg, see day) is a translation of Latin dies Martis (source of Italian martedi, French Mardi) "Day of Mars," from the Roman god of war, who was identified with Germanic Tiw (though etymologically Tiw is related to Zeus), itself a loan-translation of Greek Areos hēmera. In cognate German Dienstag and Dutch Dinsdag, the first element would appear to be Germanic ding, þing "public assembly," but it is now thought to be from Thinxus, one of the names of the war-god in Latin inscriptions.
Middle English mirie, from Old English myrge "pleasing, agreeable, pleasant, sweet, exciting feelings of enjoyment and gladness" (said of grass, trees, the world, music, song); also as an adverb, "pleasantly, melodiously," from Proto-Germanic *murgijaz, which probably originally meant "short-lasting," (compare Old High German murg "short," Gothic gamaurgjan "to shorten"), from PIE root *mregh-u- "short." The only exact cognate for meaning outside English was Middle Dutch mergelijc "joyful."
The connection to "pleasure" likely was via the notion of "making time fly, that which makes the time seem to pass quickly" (compare German Kurzweil "pastime," literally "a short time;" Old Norse skemta "to amuse, entertain, amuse oneself," from skamt, neuter of skammr "short"). There also was a verbal form in Old English, myrgan "be merry, rejoice." For vowel evolution, see bury (v.).
Not originally applied to humorous moods or speech or conduct, yet the word had a much wider senses in Middle English than modern: "pleasant-sounding" (of animal voices), "fine" (of weather), "handsome" (of dress), "pleasant-tasting" (of herbs). The evolution of the modern senses is probably via the meaning "pleased by a certain event or situation or state of things" (c. 1200). Of persons, "cheerful by disposition or nature; playfully cheerful, enlivened with gladness or good spirits," by mid-14c.
Merry-bout "an incident of sexual intercourse" was low slang from 1780. Merry-begot "illegitimate" (adj.), also "bastard" (n.) are in Grose (1785). Merrie England (now frequently satirical or ironic) is c. 1400, meri ingland, originally in a broader sense of "bountiful, prosperous." Merry Monday was a 16c. term for "the Monday before Shrove Tuesday" (Mardi Gras).
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"]