Etymology
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*pleu- 
Proto-Indo-European root meaning "to flow."

It forms all or part of: fletcher; fledge; flee; fleet (adj.) "swift;" fleet (n.2) "group of ships under one command;" fleet (v.) "to float, drift; flow, run;" fleeting; flight (n.1) "act of flying;" flight (n.2) "act of fleeing;" flit; float; flood; flotsam; flotilla; flow; flue; flugelhorn; fluster; flutter; fly (v.1) "move through the air with wings;" fly (n.) "winged insect;" fowl; plover; Pluto; plutocracy; pluvial; pneumo-; pneumonia; pneumonic; pulmonary.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit plavate "navigates, swims;" Greek plynein "to wash," plein "to navigate," ploein "to float, swim," plotos "floating, navigable," pyelos "trough, basin;" Latin plovere "to rain," pluvius "rainy;" Armenian luanam "I wash;" Old English flowan "to flow;" Old Church Slavonic plovo "to flow, navigate;" Lithuanian pilu, pilti "to pour out," plauju, plauti "to swim, rinse."
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nod (v.)

late 14c., "to quickly bow the head; to assent, beckon, or salute quickly by an inclination of the head," late 14c., nodden, a word of unknown origin, probably an Old English word, but not recorded, or perhaps from a Low German word related to Old High German hnoton "to shake," from Proto-Germanic *hnudan (OED considers this "doubtful"). Apparently unrelated to Latin nuere "to nod." Related: Nodded; nodding

Meaning "droop the head forward with a short, involuntary motion," as when drowsy, is by 1560s. Figurative sense of "be guilty of a lapse, be momentarily inattentive" is by 1670s, echoing Horace's dormitat Homerus. Of flowers, etc., "to droop or bend downward," c. 1600. Meaning "to drift in and out of consciousness while on drugs" is attested by 1968 (as a noun in this sense by 1942).

A nodding acquaintance (by 1821) is one you know just well enough to recognize with a nod. Land of Nod "state of sleep" (1731) is a pun on the biblical place name east of Eden (Genesis iv.16). 

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continental (adj.)

1818 as a purely geographical term, "relating to or of the nature of a continent," from continent (n.) + -al (1). In reference to the European mainland (as opposed to Great Britain), recorded from 1760. Continental breakfast (the kind eaten on the continent as opposed to the kind eaten in Britain) is attested by 1855.

As "pertaining to the government and affairs of the 13 revolutionary British American colonies," from 1774; the Continental Congress was so called from 1775.

Continental divide "line across a continent such that the drainage on one side feeds into one ocean or sea and that on the other feeds into a different body of water," was in use by 1865; continental slope "slope between the outer edge of the continental shelf and the ocean floor" is from 1849. Continental shelf "area of shallow sea around a continent, geologically part of the continent" is first attested 1888.

Continental drift "gradual movement of the continents across the earth's surface through geological time" (1925) is a translation of German Kontinentalverschiebung, proposed 1912 by German scientist Alfred Wegener (1880-1930); the theory was not widely accepted until after c. 1950.

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tunnel (n.)

early 15c., tonel, "funnel-shaped net for catching birds," from Old French tonnelle "net," or tonel "cask," diminutive of Old French tonne "tun, cask for liquids," possibly from the same source as Old English tunne (see tun).

Sense of "tube, pipe" (1540s) developed in English and led to sense of "underground passage" (1660s). This sense subsequently has been borrowed into French (1878). The earlier native word for this was mine (n.). Meaning "burrow of an animal" is from 1873. Tunnel vision is attested from 1912. The amusement park tunnel of love is attested from 1911 (in reference to New York's Luna Park). The figurative light at the end of the tunnel has been seen since 1882.

The "Tunnel of Love," an attraction found at many amusement parks, has been responsible for a surprising number of proposals. In this and similar devices, couples are allowed to drift through dark or semi-dark underground caverns, usually in a boat or gondola borne on an artificial stream of water. ... Their dim interiors often give a bashful young man the opportunity to propose. [The American Magazine, July 1922]
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pink (n., adj.)

1570s, common name of Dianthus, a garden plant of various colors; a word of unknown origin. It is perhaps from pink (v.) via the notion of "perforated" (scalloped) petals. Or perhaps it is from Dutch pink "small, narrow" (see pinkie), itself obscure, via the term pinck oogen "half-closed eyes," literally "small eyes," which was borrowed into English (1570s) and may have been used as a name for Dianthus, which sometimes has small dots resembling eyes.

The noun meaning "pale red color, red color of low chroma but high luminosity" is recorded by 1733 (pink-coloured is recorded from 1680s), from one of the common colors of the flowers.  The adjective pink is attested by 1720. As an earlier name for such a color English had incarnation "flesh-color" (mid-14c.), and as an adjective incarnate (1530s), from Latin words for "flesh" (see incarnation) but these also had other associations and tended to drift in sense from "flesh-color, blush-color" toward "crimson, blood color."

The flower meaning led (by 1590s) to a figurative use for "the flower" or highest type or example of excellence of anything (as in Mercutio's "Nay, I am the very pinck of curtesie," Rom. & Jul. II.iv.61). Compare flour (n.). The political noun sense "person perceived as left of center but not entirely radical (i.e. red)" is attested by 1927, but the image dates to at least 1837. Pink slip "discharge notice" is attested by 1915; pink slips had various connotations in employment in the first decade of the 20th century, including a paper signed by a worker to testify he would leave the labor union or else be fired. To see pink elephants "hallucinate from alcoholism" is from 1913 in Jack London's "John Barleycorn."

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cousin (n.)

early 13c., "a collateral blood relative more remote than a brother or sister" (mid-12c. as a surname), from Old French cosin "nephew; kinsman; cousin" (12c., Modern French cousin), from Latin consobrinus "cousin," originally "mother's sister's son," from assimilated form of com "with, together" (see com-) + sobrinus (earlier *sosrinos) "cousin on mother's side," from soror (genitive sororis) "sister" (see sister).

Specific modern usage, "the son or daughter of an uncle or aunt," is attested by c. 1300, but throughout Middle English the word also was used of grandchildren, godchildren, etc. Extended sense of "closely related thing" is from late 14c.

Italian cugino, Danish kusine, Polish kuzyn also are from French. German vetter is from Old High German fetiro "uncle," perhaps on the notion of "child of uncle." Words for cousin tend to drift to "nephew" on the notion of "father's nephew."

Many IE languages (including Irish, Sanskrit, Slavic, and some of the Germanic tongues) have or had separate words for some or all of the eight possible "cousin" relationships, such as Latin, which along with consobrinus had consobrina "mother's sister's daughter," patruelis "father's brother's son," atruelis "mother's brother's son," amitinus "father's sister's son," etc. Old English distinguished fæderan sunu "father's brother's son," modrigan sunu "mother's sister's son," etc.

Used familiarly as a term of address since early 15c., especially in Cornwall. Phrase kissing cousin is a Southern U.S. expression, 1940s, apparently denoting "those close enough to be kissed in salutation;" Kentish cousin (1796) is an old British term for "distant relative." For cousin german "first cousin" (early 14c.) see german (adj.).

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