by 1884, from French mal du sìecle, "world-weariness, atrophy of the spirit, aristocratic boredom, deep melancholy over the condition of the world," supposedly a characteristic condition of young romantics in Europe in the early 19c. It answers to German Weltschmerz.
mid-14c., also simply coat (mid-14c.); originally a tunic embroidered or painted with heraldic armorial bearings (worn over armor, etc); see coat (n.) + arm (n.2) and compare Old French cote a armer. Sense transferred in Middle English to the heraldic arms themselves. Hence turncoat, one who put his coat on inside-out to hide the badge of his loyalty (1550s).
"the spirit of the sea," 1751, first mentioned in Smollett's "The Adventures of Peregrin Pickle" as ("according to the mythology of sailors") an ominous and terrifying fiend who "presides over all the evil spirits of the deep, and is often seen in various shapes, perching among the rigging on the eve of hurricanes, shipwrecks and other disasters." Davy Jones's Locker "bottom of the sea," is 1803, from nautical slang, of unknown origin; second element may be from biblical Jonah, regarded as unlucky by sailors.