Online Etymology Dictionary

under (prep., adv.): O.E. under, from P.Gmc. *under- (cf. O.Fris. under, Du. onder, O.H.G. untar, Ger. unter, O.N. undir, Goth. undar), from PIE *ndhero- "lower" (cf. Skt. adhah "below;" Avestan athara- "lower;" L. infernus "lower," infra "below"). Notion of "subordination" was present in O.E. Also used in O.E. as a preposition meaning "between, among," as still in under these circumstances, etc. (though this may be an entirely separate root; see understand). Productive as a prefix in O.E. times, as in Ger. and Scand. Under the table is from 1921 in the sense of "very drunk," 1940s in sense of "illegal." To get something under (one's) belt is from 1954; to keep something under (one's) hat "secret" is from 1885; to have something under (one's) nose "in plain sight" is from 1548; to speak under (one's) breath "in a low voice" is attested from 1832. To be under (someone's) thumb "entirely controlled" is recorded from 1754.
under-achiever: 1953, from under + achiever (see achieve). Under-achievement is recorded from 1951.
under-age (adj.): 1594, from under + age.
under-employed: 1908, "not used to optimum capacity," originally in ref. to working persons, from under + pp. of employ.
under-nourished: 1910, from under + pp. of nourish.
under-rate: 1650, "to esteem at too little worth," from under + rate (v.).
under-sea: 1613, from under + sea.
under-utilize: 1954, from un- (1) "not" + pp. of utilize.
underarm: 1816, "underhand" (in ref. to a style of throwing), from under + arm. First attested 1908 in dressmaking sense of "seams on the lower half of the arm-hole;" as a euphemism for armpit, it is attested from 1930s, popularized by advertisers.
underbelly: 1607, from under + belly. In fig. sense of "most vulnerable part" it is recorded from Churchill's 1942 speech. Sometimes used erroneously in sense of "seamy or sordid part" of anything.
underbred: "of inferior breeding, vulgar," 1650, from under + pp. of breed (v.). Of animals, "not pure bred," attested from 1890.
underbrush: 1775, "shrub and small trees in a forest," from under + brush (n.). Originally Amer.Eng.; cf. undergrowth, attested in the same sense from 1600.
undercarriage: 1794, from under + carriage. Meaning "landing gear of an aircraft" is recorded from 1911.
underclass: "subordinate social class," 1918, from under + class (n.). A loan-translation of Swed. underklass.
underclassman: "sophomore or freshman," 1896, from under + class in the school form sense + man.
undercover: 1854, sheltered," from under + cover. Sense of "operating secretly" attested from 1920.
undercurrent: 1663, "stream of water or air flowing beneath the surface or beneath another current," a hybrid formed from under + current. The fig. sense of "suppressed or underlying character" is attested from 1817.
undercut (v.): 1382, "to cut down or off," from under + cut (v.). In the commercial sense of "to sell at lower prices" (or work at lower wages) it is first attested 1884. Fig. sense of "render unstable, undermine" is recorded from 1955, from earlier lit. meaning "cut so as to leave the upper portion larger than the lower" (1874).
underdeveloped: 1892, in the photography sense, under + pp. of develop. In ref. to countries or regions, recorded from 1949.
underdog: "the beaten dog in a fight," 1887, from under + dog. Cf. top dog "dominant person in a situation or hierarchy."
underdone: 1680s, in reference to cooked meat, from under + p.p. of do.
underdressed: "too plainly dressed," 1784, from under + pp. of dress (v.).
underestimate (v.): 1812, "to estimate at too low an amount," from under + estimate (v.). Meaning "to rank too low, undervalue" is recorded from 1850.
underfoot (adv.): c.1200, underfot "under the feet," from under + foot. Cf. M.Du. ondervoete. As an adj., attested from 1596; in ref. to persons, "continually in the way," it is recorded from 1891.
undergo: O.E. undergan "undermine," from under + gan (see go). Cf. M.Du. ondergaen, O.H.G. untarkun, Ger. untergehen, Dan. undergaa. Sense of "submit to, endure" is attested from c.1300. Meaning "to pass through" (an alteration, etc.) is attested from 1634.
undergraduate: 1630, a hybrid formed from under + graduate (n.). British used fem. form undergraduette in 1920s-30s.
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.
undergrowth: 1600, from under + growth (see grow).
underhand (adv.): O.E. under hand "in subjection," from under + hand. Sense of "secret, stealthy, surreptitious" first recorded 1538. For sense development, cf. M.Du. onderhanden "by degrees, slowly," Du. onderhandsch "secret, private." The adj. is attested from 1545.
underlay: O.E. under lecgan "to support by placing something beneath;" see under + lay (v.).
underlie: O.E. under licgan "to be subordinate to, to submit to;" see under + lie (v.2). Meaning "to lie under or beneath" is attested from 1600; fig. sense of "to be the basis of" is attested from 1852 (implied in underlying).
underline (v.): 1721, from under + line (v.). Cf. Du. onderlijnen. The noun is attested from 1888.
underling: c.1175, from under + dim. suffix -ling.
undermine: c.1300, undermyne, from under + mine (v.). The fig. sense is attested from c.1430. Cf. Du. ondermijnen, Dan. underminere, Ger. unterminiren.
underneath: O.E. underneoðan, from under + neoðan "below" (see beneath).
underpants: 1931, from under + pants. Drove out drawers, knickers in this sense.
underpass: 1904, Amer.Eng., from under + pass.
underpinning: 1489, "action of supporting or strengthening from beneath," from under + pp. of pin (v.). Fig. sense of "prop, support" is recorded from 1589.
underprivileged (adj.): 1896, from under + pp. of privilege (v.). Noun use is attested from 1935.
underscore (v.): 1771, "to draw a line under," from under + score (v.). The fig. sense of "to emphasize" is attested from 1891. Noun meaning "a line drawn below (something)" is recorded from 1901.
undershirt: 1648, from under + shirt. Cf. N.Fris. onnersjürt, Dan. underskjorte.
undershoot: 1661, "to shoot too low," from under + shoot (v.). In ref. to aircraft or pilots, recorded from 1918. Undershot as a type of water wheel is recorded from 1610.
underside: c.1680, from under + side (n.). Cf. Du. onderzijde, Dan. underside, Ger. unterseite.
undersign (v.): 1580, from under + sign (v.).
understand: O.E. understandan "comprehend, grasp the idea of," probably lit. "stand in the midst of," from under + standan "to stand" (see stand). If this is the meaning, the under is not the usual word meaning "beneath," but from O.E. under, from PIE *nter- "between, among" (cf. Skt. antar "among, between," L. inter "between, among," Gk. entera "intestines;" see inter-). But the exact notion is unclear. Perhaps the ult. sense is "be close to," cf. Gk. epistamai "I know how, I know," lit. "I stand upon." Similar formations are found in O.Fris. (understonda), M.Dan. (understande), while other Gmc. languages use compounds meaning "stand before" (cf. Ger. verstehen, represented in O.E. by forstanden ). For this concept, most I.E. languages use fig. extensions of compounds that lit. mean "put together," or "separate," or "take, grasp."
understanding: O.E. understandincge "comprehension," from understand (q.v.). Meaning "mutual agreement" is attested from 1803.
understatement: 1799, from under + statement. Understated, with ref. to clothing, is recorded from 1957.
understorey: 1945, in ref. to forest vegetation, from under + storey.
understudy (v.): 1874, in the theatrical sense, from under + study (v.). The noun is attested from 1882.