1909 as a heraldic animal, 1964 as a U.S. proprietary name for brine shrimp (Artemia salina), which had been raised as food for aquarium fish but were marketed as pets by U.S. inventor Harold von Braunhut (1926-2003), who also invented "X-Ray Specs" and popularized pet hermit crabs. He began marketing them in comic book advertisements in 1960 as "Instant Life," and changed the name to Sea Monkeys in 1964, so called for their long tails.
lake of the River Jordan, mid-13c., from dead (adj.); its water is 26 percent salt (as opposed to 3 or 4 percent in most oceans) and supports practically no life. In the Bible it was the "Salt Sea" (Hebrew yam hammelah), also "Sea of the Plain" and "East Sea." In Arabic it is al-bahr al-mayyit "Dead Sea." The ancient Greeks knew it as he Thalassa asphaltites "the Asphaltite Sea." Latin Mare Mortum, Greek he nekra thalassa (both "The Dead Sea") referred to the sea at the northern boundaries of Europe, the Arctic Ocean.
"the sea; naturally occurring salt water," late Old English sealtera watera. As an adjective from 1520s, "inhabiting salt water or the sea." Salt-water taffy attested by 1886; so called because it originally was sold at seashore resorts, especially Atlantic City, N.J. (see taffy).
"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." The second element in the name might be from biblical Jonah, regarded as unlucky by sailors.
Davy Jones's Locker "bottom of the sea," is by 1803 (Davy's locker in the same sense is by 1788), from nautical slang, of unknown origin.
slang for "drunk," 1736, sometimes said to be from notion of a ship heavy-laden and so low in the water that small waves (half seas) wash over the deck. This suits the sense, but the phrase is not recorded in this alleged literal sense. Half seas over "halfway across the sea" is recorded from 1550s, however, and it was given a figurative extension to "halfway through a matter" by 1690s. What drunkenness is halfway to is not clear.
c. 1600, "part of the Italian mainland ruled by Venice," from Modern Latin terra firma, literally "firm land," from Latin terra "earth, land" (from PIE root *ters- "to dry") + firma, fem. of firmus "strong, steadfast" (from suffixed form of PIE root *dher- "to hold firmly, support"). Meaning "the land" (as distinct from "the sea") is first attested 1690s. Hakluyt and Sandys also used English firm (n.) to mean "the firm land, the mainland, terra firma."
"place where something is discarded," by 1921 (in phrase give (something) the deep six), originally in motorboating slang, perhaps from earlier underworld noun sense of "the grave" (1929), which is perhaps a reference to the usual grave depth of six feet. But the phrase (in common with mark twain) also figured in sailing jargon, of sounding, for a measure of six fathoms:
As the water deepened under her keel the boyish voice rang out from the chains: "By the mark five—and a quarter less six—by the deep six—and a half seven—by the deep eight—and a quarter eight." ["Learning the Road to Sea," in Outing magazine, February 1918]
In general use by 1940s. As a verb from 1953.