Etymology
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sink (n.)

early 15c., "cesspool, pit for reception of wastewater or sewage," from sink (v.). The meaning "drain for carrying water to a sink" is from late 15c., and the sense of "shallow basin (especially in a kitchen) with a drainpipe for carrying off dirty water" is by 1560s.

The figurative sense of "place where corruption and vice abound, abode or resort of depraved or debauched persons" is from 1520s.  In science and technical use, "place where heat or other energy is removed from a system" (opposite of source), from 1855, from the notion of sink as "receptacle of waste matter."

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pool (n.2)

game similar to billiards, 1848, originally (1690s) the name of a card game played for collective stakes, from pool "collective stakes of players in a game," which is from French poule "stakes, booty, plunder," literally "hen," from Old French poille "hen, young fowl," from Vulgar Latin *pulla, fem. of Latin pullus "young animal," especially "young fowl," from PIE root *pau- (1) "few, little."

Perhaps the original notion is from jeu de la poule, supposedly a game in which people threw things at a chicken and the player who hit it, won it, which speaks volumes about life in the Middle Ages. The notion behind the word, then, is "playing for money." The connection of "hen" and "stakes" is also present in Spanish polla and Walloon paie.

By 1868 it came to mean "combination of a number of persons, each staking a sum of money on the success of a horse in a race, a contest in a game, etc., the money to be divided among the successful bettors," thus also "collective stakes" in betting. The sense of "common reservoir of resources" is from 1917. Meaning "group of persons who share duties or skills" (typist pool, etc.) is from 1928. From 1933 as short for football pool in wagering.

Pool shark is from 1898. The phrase dirty pool "underhanded or unsportsmanlike conduct," especially in politics (1951), seems to belong here now, but the phrase dirty pool of politics, with an image of pool (n.1) is recorded from 1871 and was in use early 20c.

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dag (n.)

several words, probably unrelated, including: 1. "pendant point of cloth on a garment," late 14c., of uncertain origin; 2. "thin rain, drizzle, wet fog," Scottish, late 17c., from a Scandinavian source such as Old Norse dögg, plural daggir "dew," from Proto-Germanic *daowo- (source of Old English deaw; see dew); 3. "kind of heavy pistol," 1560s, of uncertain origin; 4. "clot of dirty wool about the rear end of a sheep," 1731; 5. "tough but amusing person," Australian and New Zealand slang, 1916.

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toil (n.1)

"hard work," c. 1300, originally "turmoil, contention, dispute," from Anglo-French toil (13c.), from toiler "agitate, stir up, entangle, writhe about," from Old French toeillier "drag about, make dirty" (12c.), usually said to be from Latin tudiculare "crush with a small hammer," from tudicula "mill for crushing olives, instrument for crushing," from Latin tudes "hammer," from PIE *tud-, variant of *(s)teu- "to push, stroke, knock, beat" (see obtuse). Sense of "hard work, labor" (1590s) is from the related verb (see toil (v.)).

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pollution (n.)

mid-14c., pollucioun, "discharge of semen other than during sex," later, "desecration, profanation, defilement, legal or ceremonial uncleanness" (late 14c.), from Late Latin pollutionem (nominative pollutio) "defilement," noun of action from past-participle stem of Latin polluere "to soil, defile, contaminate," probably from *por- "before" (a variation of pro "before, for;" see pro-) + -luere "smear," from PIE root *leu- "dirt; make dirty" (see lutose). Sense of "contamination of the environment" is recorded from c. 1860, but not common until c. 1955.

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Sparta 

capital of Laconia in ancient Greece, famed for severity of its social order, the frugality of its people, the valor of its arms, and the brevity of its speech. Also for dirty boys, men vain of their long hair, boxing girls, iron money, and insufferable black broth. The name is said to be from Greek sparte "cord made from spartos," a type of broom, from PIE *spr-to-, from root *sper- (2) "to turn, twist" (see spiral (adj.)). Perhaps the reference is to the cords laid as foundation markers for the city. Or the whole thing could be folk etymology.

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glory hole (n.)

1825, "drawer or box where things are heaped together in a disorderly manner." The first element probably is a variant of Scottish glaur "to make muddy, dirty, defile" (Middle English glorien, mid-15c.), which is perhaps from Old Norse leir "mud." Hence, in nautical use, "a small room between decks," and, in mining, "large opening or pit." Meaning "opening through which the interior of a furnace may be seen and reached" (originally in glassblowing) is from 1849, probably from glory (n.), which had developed a sense of "circle or ring of light" by 1690s. Sexual (originally homosexual) sense from 1940s.

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smudge (v.)

early 15c., smogen "to soil, smear or stain with dirt or filth, blacken," a word of obscure origin. Compare smutch and its variant smouch, Middle English smod "filth, obscene behavior" (mid-13c., also a surname); Middle Dutch besmodden, smoddich, Middle Low German smudden.

The meaning "to rub out or in" is by 1865. Related: Smudged; smudging. The noun meaning "a dirty mark or stain, spot, smear" is attested by 1768, from the verb.

The smudge meaning "make a smoky fire" is by 1860, also of unknown origin, but perhaps related. According to OED now dialectal and North American. OED also gives it in an earlier, obsolete sense of "cure (herring, etc.) by smoking" (1590s).

The related noun smudge is attested by 1767 as "a suffocating smoke" (to repel mosquitoes, etc.); from 1806 as "heap of combustibles ignited and emitting dense smoke." Hence smudge-pot (1903). Smudge-stick as a Native American (Crow tribe) artifact is by 1908

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mud (n.)

late 14c., mudde, "moist, soft earth," cognate with and probably from Middle Low German mudde, Middle Dutch modde "thick mud," from Proto-Germanic *mud- from PIE *(s)meu-/*mu- [Buck], found in many words denoting "wet" or "dirty" (source also of Greek mydos "damp, moisture," Old Irish muad "cloud," Polish muł "slime," Sanskrit mutra- "urine," Avestan muthra- "excrement, filth"); related to German Schmutz "dirt," which also is used for "mud" in roads, etc., to avoid dreck, which originally meant "excrement." Welsh mwd is from English. The older word is fen.

Meaning "lowest or worst of anything" is from 1580s. As a word for "coffee," it is hobo slang from 1925; as a word for "opium" from 1922. Mud-puppy "salamander" is by 1855, American English; the mud-dauber wasp was so called by 1856. The children's mud-pie is attested from 1788. Mud-flat "muddy, low-lying ground near a shore" is by 1779. Mud-room "room for removing wet or muddy footwear" is by 1938.

The expression clear as mud (that is, "not clear at all") is by 1796. To throw or hurl mud "make disgraceful accusations" is from 1762. To say (one's) name is mud and mean "(one) is discredited" is recorded from 1823, from mud in obsolete sense of "a stupid twaddling fellow" (1708). Mud in your eye as a toast is recorded from 1912, American English.

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defile (v.)

c. 1400, "to desecrate, profane;" mid-15c., "to make foul or dirty," also "to rape, deflower," alteration of earlier defoulen, from Old French defouler "trample down, violate," also "ill-treat, dishonor," from de- "down" (see de-) + foler "to tread," from Latin fullo "person who cleans and thickens cloth by stamping on it" (see foil (v.1)).

The alteration (or re-formation) in English is from influence of Middle English filen (v.) "to render foul; make unclean or impure," literal and figurative, from Old English fylen (trans.), related to Old English fulian (intrans.) "to become foul, rot," from the source of foul (adj.). Compare befoul, which also had a parallel form befilen. Related: Defiled; defiling.

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