Online Etymology Dictionary

underground (adv.): 1571, "below the surface," from under + ground (n.). Adj. is attested from 1610; fig. sense of "hidden, secret" is attested from 1632; adj. meaning "subculture" is from 1953, from World War II application to resistance movements against German occupation, on analogy of the dominant culture and Nazis. Noun sense of "underground railway" is from 1887 (phrase underground railway itself is attested from 1834).
Underground Railroad: "network of U.S. anti-slavery activists helping runaways elude capture," attested from 1852 but said to date from 1831, coined in jest by bewildered trackers after their slaves vanished without a trace.
subway: 1825, "underground passage" (for water pipes or pedestrians), from sub- + way. The sense of "underground railway in a city" is first recorded 1893, in ref. to Boston.
fluffer: "track sweeper on the London underground," by 1956.
tunnel (n.): c.1440, "funnel-shaped net for catching birds," from M.Fr. tonnelle "net," or tonel "cask," dim. of O.Fr. tonne "tun, cask for liquids," possibly from the same source as O.E. tunne (see tun). Sense of "tube, pipe" (1545) developed in Eng. and led to sense of "underground passage," which is first attested 1765, about five years after the first modern tunnel was built (on the Grand Trunk Canal in England). This sense subsequently has been borrowed into Mod.Fr. (1878). The earlier native word for this was mine. Meaning "burrow of an animal" is from 1873. The verb meaning "excavate underground" is first attested 1795. Tunnel vision first recorded 1949. The fig. phrase light at the end of the tunnel is attested from 1922.
Metro: Paris underground, 1904, from Fr. abbrev. of Chemin de Fer Métropolitain "Metropolitan Railway."
bose: "to seek for hollows underground by ramming the ground and observing the vibrations," 1929, ult. from Scottish word boss "hollow, empty" (1510s), earlier a noun meaning "small cask, wine flask" (late 14c.).
U-bahn: Ger. or Austrian subway system, 1938 (originally in ref. to Berlin), from Ger. U-bahn, short for Untergrund-bahn, lit. "underground railway."
tuber: "thick underground stem," 1668, from L. tuber "lump, bump," perhaps related to tumere "to swell" (see thigh).
sink-hole: as a geological phenomenon, "hole made in the earth by underground erosion," 1780, from sink (v.) + hole.
subterranean: c.1600, from L. subterraneus "underground," from sub "under" + terra "earth" (see terrain).
Vaseline: 1872, trademark for an ointment made from petroleum and marketed by Chesebrough Manufacturing Co., coined from Ger. Wasser "water" + Gk. elaion "oil" + scientific-sounded ending -ine. Robert A. Chesebrough was of the opinion that petroleum was a product of the underground decomposition of water.
crypt: early 15c., "grotto, cavern," from L. crypta "vault, cavern," from Gk. krypte, fem. of kryptos "hidden," from kryptein "to hide." Meaning "underground burial vault or chapel in a church" first attested 1789.
dungeon: c.1300, from O.Fr. donjon "great tower of a castle," from Gallo-Romance *dominionem, from L.L. dominium, from L. dominus "master" (of the castle; see domain). Sense of "castle keep" led to "strong (underground) cell" in Eng. pre-1338.
bulb: 1560s, "an onion," from M.Fr. bulbe, from L. bulbus "bulb, onion," from Gk. bolbos "plant with round swelling on underground stem." Expanded by 1800 to "swelling in a glass tube" (thermometer bulb, light bulb, etc.).
silo: 1835, from Sp. silo, from L. sirum (nom. sirus), from Gk. siros "a pit to keep corn in." Or, alternately, the Sp. word is from a pre-Roman Iberian language word represented by Basque zilo, zulo "dugout, cave or shelter for keeping grain." Meaning "underground housing and launch tube for a guided missile" is attested from 1958.
overground (adj.): "situated above ground" (as opposed to underground), 1879, from over + ground (n.).
catacomb: O.E. catacumbas, from L.L. (400 C.E.) catacumbae, originally the region of underground tombs between the 2nd and 3rd milestones of the Appian Way (where the bodies of apostles Paul and Peter were said to have been laid), origin obscure, perhaps once a proper name, or dissimilation from L. cata tumbas "at the graves," from cata- "among" + tumbas, acc. pl. of tumba "tomb." Extended 1836 to any subterranean receptacle of the dead (as in Paris).
rhabdomancy: 1646, "use of divining rod" (especially to discover ores or underground water), from Gk. rhabdos "rod, twig, stick" + manteia "divination, oracle." Gk. rhabdos is from PIE *werbh- (cf. Lith. virbas "twig, branch, scion, rod," L. verbena "leaves and branches of laurel"), from base *werb- "to turn, bend" (see warp).
cistern: mid-13c., from O.Fr. cisterne, from L. cisterna "underground reservoir for water," from cista "chest," from Gk. kiste "box, chest" (see chest).
dung: O.E. dung "manure," from PIE *dhengh- "covering" (cf. Lith. dengti "to cover," O.Ir. dingim "I press"); the word recalls the ancient Gmc. custom (reported by Tacitus) of covering underground shelters with manure to keep in warmth in winter.
"The whole body of journeymen tailors is divided into two classes, denominated Flints and Dungs: the former work by the day and receive all equal wages; the latter work generally by the piece" [1824].
metropolitan: early 15c., as a noun, "bishop having oversight of other bishops," from L.L. metropolitanus, from Gk. metropolis "mother city" (from which others have been colonized), from meter "mother" + polis "city" (see policy (1)). In Gk., "parent state of a colony;" later, "see of a metropolitan bishop." In the West, the position now roughly corresponds to archbishop, but in the Greek church it ranks above it. In English, the adj. sense of "belonging to an ecclesiastical metropolis" is from 1540s; that of "belonging to a chief or capital city" is from 1550s. In reference to underground city railways, it is attested from 1867.
Pict: an ancient people of Great Britain, late 14c., from L.L. Picti (late 3c., probably a nickname given them by Roman soldiers), usually taken as derived from picti "painted," but probably ultimately from the Celtic name of the tribe, perhaps Pehta, Peihta, lit. "the fighters" (cf. Gaul. Pictavi, who gave the name to the French city of Poitiers). They painted and tattooed themselves, which may have suggested a Roman folk-etymology alteration of the name. The O.E. name for the people was Peohtas.
"In Scottish folk-lore the Pechts are often represented as a dark pygmy race, or an underground people; and sometimes identified with elves, brownies, or fairies." [OED]
character: early 14c., from O.Fr. caractere, from L. character, from Gk. kharakter "engraved mark," from kharassein "to engrave," from kharax "pointed stake." Meaning extended by metaphor to "a defining quality."
"You remember Eponina, who kept her husband alive in an underground cavern so devotedly and heroically? The force of character she showed in keeping up his spirits would have been used to hide a lover from her husband if they had been living quietly in Rome. Strong characters need strong nourishment." [Stendhal, "De l'Amour" 1822]
Sense of "person in a play or novel" is first attested 1660s, in reference to the "defining qualities" he or she is given by the author. The Latin ch- spelling was restored 1500s.
root (n.): "underground part of a plant," late O.E. rot, from O.N. rot "root," from P.Gmc. *wrot, *vrot (with characteristic loss of -w- before -r-), from PIE *wrd-. The O.E. cognate was wyrt "root, herb, plant" (see wort); also cognate with L. radix. The usual O.E. words for "root" were wyrttruma and wyrtwala. Figurative use is from c.1200. Of teeth, hair, etc., from early 13c. Mathematical sense is from 1550s. Slang meaning "penis" is recorded from 1846. The verb meaning "fixed or firmly attached by roots" (often figurative) is attested from late 14c.; sense of "to pull up by the root" (now usually uproot) also is from late 14c. Root beer first recorded 1843, Amer.Eng.; root doctor is from 1821.
tank (n.): 1610s, "pool or lake for irrigation or drinking water," a word originally brought by the Portuguese from India, ultimately from Gujarati tankh "cistern, underground reservoir for water," Marathi tanken, or tanka "reservoir of water, tank." Perhaps from Skt. tadaga-m "pond, lake pool," and reinforced in later sense of "large artificial container for liquid" (1690) by Port. tanque "reservoir," from estancar "hold back a current of water," from V.L. *stanticare (see stanch). But others say the Port. word is the source of the Indian ones. Meaning "fuel container" is recorded from 1902. Military use originated 1915, partly as a code word, partly because they looked like benzene tanks. They were first used in action at Pozieres ridge, on the Western Front, Sept. 15, 1916. Slang meaning "detention cell" is from 1912.