(A). A policeman. Said to be so called from the copper badge which Fernando Wood, of New York, appointed them to wear; but more likely a variant of “cop” (q.v.).
“There were cries of `Coppers, Coppers!' in the yard, and then a violent struggle. ... Whoever it was that was wanted had been evidently secured and dragged off to gaol.'” —T. Terrell: Lady Delmar, 1.
Copper was by the ancient alchemists called Venus; gold, symbol of Apollo (the sun); silver, of Diana (the moon); iron, of Mars; quicksilver, of Mercury; tin, of Jupiter; and lead, of Saturn.
Give us a copper, i.e. a piece of copper money. I have no coppers—no ha'pence.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Copper from Fact Monster: