Etymology
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copper (n.1)

malleable metallic element, noted for its peculiar red color, tenacity, malleability, and electric conductivity, late Old English coper, from Proto-Germanic *kupar (source also of Middle Dutch koper, Old Norse koparr, Old High German kupfar), from Late Latin cuprum, contraction of Latin Cyprium (aes) "Cyprian (metal)," after Greek Kyprios "Cyprus" (see Cyprus).

Ancient Greek had khalkos "ore, copper, bronze;" an old IE word for "ore, copper, bronze" is retained in Sanskrit ayah, Latin aes. Latin aes originally was "copper," but this was extended to its alloy with tin (see bronze), and as this was far more extensively used than pure copper, the word's primary sense shifted to the alloy and a new word evolved for "copper," from the Latin form of the name of the island of Cyprus, where copper was mined (the alchemists associated copper with Venus).

Aes passed into Germanic (which originally did not distinguish copper from its alloys) and became English ore. In Latin, aes was the common word for "cash, coin, debt, wages" in many figurative expressions. Chemical symbol Cu is from cuprum.

As "a copper coin," from 1580s; as "a vessel made of copper," 1660s. The adjective, "of or resembling copper," is from 1570s; the verb, "to cover with copper" is from 1520s.

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copper (n.2)

"policeman," 1846; probably an agent noun from the verb cop "to seize, to catch, capture or arrest as a prisoner" (see cop (v.)).

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copper-nickel (n.)

alloy of copper that contains nickel, used in coinage, etc., 1728; see copper (n.1) + nickel.

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coppersmith (n.)

also copper-smith, "artisan who works in copper," early 14c., c. 1300 as a surname," from copper (n.1) + smith.

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copperplate (n.)

also copper-plate, "plate of polished copper, engraved and etched," 1660s, from copper (n.1) + plate (n.).

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cupreous (adj.)

1660s, "consisting of or containing copper," from Late Latin cupreus "of copper," from cuprum, alternative form of cyprum "copper" (see copper (n.1)). Meaning "copper-colored" is by 1804. Related: Cupric (1799).

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era (n.)
1716, earlier aera (1610s), from Late Latin aera, era "an era or epoch from which time is reckoned" (7c.), probably identical with Latin aera "counters used for calculation," plural of aes (genitive aeris) "brass, copper, money" (see ore, also compare copper). The Latin word's use in chronology said to have begun in 5c. Spain (where the local era, aera Hispanica, began 38 B.C.E.; some say because of a tax levied that year). Other ancient eras included the Chaldean (autumn of 311 B.C.E.), the Era of Actium (31 B.C.E.), of Antioch (49 B.C.E.), of Tyre (126 B.C.E.), the Olympiadic (July 1, 776 B.C.E.) and the Seleucidan (autumn 312 B.C.E.). In English it originally meant "the starting point of an age" (compare epoch); meaning "system of chronological notation" is from 1640s; that of "historical period" is from 1741, as in the U.S. Era of Good Feeling (1817) was anything but.
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kipper (n.)
Old English cypera "male salmon," perhaps related to coper "reddish-brown metal" (see copper (n.1)), on resemblance of color. Another theory connects it to kip (n.) "sharp, hooked lower jaw of the male salmon in breeding season," which is from Middle English kippen "to snatch, tug, pull," but OED doubts this.

The modern noun usually is a shortening of kippered herring, from a verb meaning "to cure a fish by cleaning, salting, and spicing it" (early 14c.). The earliest attested uses of the verb are to preparing salmon, hence the verb. The modern noun kipper is recorded from 1773 of salmon, 1863 of herring.
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cop (n.)

"policeman," 1859, abbreviation (said to be originally thieves' slang) of earlier copper (n.2), which is attested from 1846, agent noun from cop (v.) "to capture or arrest as a prisoner." Cop-shop "police station" is attested from 1941. The children's game of cops and robbers is attested from 1900.

Each child in Heaven's playground knows each other child by name.
They choose up sides as all take part in some exciting game
Like Hide=and=Seek, Red Rover, Cops and Robbers, Pris'ner's Base.
Our Lord is glad to referee their every game and race.

[John Bernard Kelly, "Heaven is a Circus," 1900]

English has many nouns cop, some archaic or obsolete, many connected more or less obscurely to Old English cop "top, summit," which is related to the source of cup (n.).

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nickel (n.)

whitish metal element, 1755, the name was coined in 1754 by Swedish mineralogist Axel von Cronstedt (1722-1765) from shortening of Swedish kopparnickel "copper-colored ore" (from which it was first obtained), a half-translation of German Kupfernickel, literally "copper demon," from Kupfer (see copper) + Nickel "demon, goblin, rascal" (a pet form of masc. proper name Nikolaus (compare English Old Nick "the devil;" see Nicholas). According to OED, the ore was so called by miners because it looked like copper but yielded none.

Meaning "coin made partly of nickel" is from 1857, when the U.S. introduced one-cent coins made of nickel to replace the old bulky copper pennies. Application to five-cent piece (originally one part nickel, three parts copper) is from 1883; in earlier circulation there were silver half-dimes. To nickel-and-dime (someone) "make or keep (someone) poor by accumulation of trifling expenses," is by from 1964 (nickels and dimes "very small amounts of money" is attested from 1893).

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