What is the literary or historical origin of the term "gold piece" to mean a gold coin? Was it used before D&D, or did D&D coin the term?
The term definitely predates D&D - the term "twenty dollar gold piece" has been in use for the $20 Double Eagle and $10 Eagle coins of the late 19th century, and also the $5 gold coin, as well.
"Gold Piece" In Print
The term is used in the Lebanon Daily News, 1 Nov 1965, of Lebanon, Pennsylvania, bottom, in an advert for old coins under the left column of text (to the right of the comics)
Four gold pieces: One (1) $20.00 gold piece, two (2) $10.00 gold pieces and one (1) $2.50 gold piece.
This alone establishes the phrase "gold piece" for gold coins in routine use prior to D&D. But let us press a little further back... say, 1913? Here's a quote from the 5 August 1913 Cedar Rapids Evening Gazette, from Cedar Rapids, Iowa, page 4, top of the third column:
The five cent piece ls the day laborer of our coinage. It la the hardest working and most successful bit at money In use In these United States. The twenty dollar gold piece Is very popular and is madly sought after In the best society; the five dollar bill has millions of friends and the hard silver dollar can be found nestling In the pocket of almost every man. But none of these like the five cent piece.
We thus have established a pattern of use for gold coins of being called "gold pieces" in the press, spanning over 5 decades; clearly not a D&D origin; not even viably a wargaming origin, for 1913 is the year of the first printing of H. G. Wells' Little Wars, the first commercially released set of wargaming rules in book form.
Searching Project Gutenberg, several ebooks have it in use...
These without clear denomination prefixed:
- Pinocchio (1883, Tr. ??? )
Author: Carlo Collodi, 1826-1890
Translator: Carol Della Chiesa, 1887-
- The Younger Set (1907)
Author: Robert W. Chambers
- A Drama on the Seashore
Author: Honore de Balzac (1799-1850)
Translator: Katharine Prescott Wormeley (1830-1908)
- Tiger Cat (1938)
Author: David H. Keller
- Pâkia (1901)
Author: Louis Becke
And several with clear denomination in dollars:
- The Corner House Girls in a Play –
How they rehearsed, how they acted, and what the play brought in
Authors: Grace Brooks Hill, R. Emmett Owen
- The Young Bank Messenger (1898)
Author: Horatio Alger, Jr
early 13c., "fixed amount, measure, portion," from O.Fr. piece (11c.), from V.L. *pettia, probably from Gaulish (cf. Welsh peth "thing," Breton pez "piece"), from O.Celt. base *pett-.
Piece of Eight is the old name for the Spanish dollar (c.1600) of the value of 8 reals.
It's pretty clear that it's a generic term for a gold coin, and for several US gold coins as well. In the US, it seems to be predominantly the popular $5 coin of the late 19th and early 20th centuries, but can be used collectively for the $2.50, $5.00, $10.00 and $20.00 gold coins; The silver coins of similar values were $0.10, $0.25, $0.50, and $1.00. Note that, still to date, "2 bits" is $0.25... a reference to the not uncommon practice of breaking Pieces of Eight (Dollares, or Reals) into 8 "bits" of an eighth-dollare each... I suspect that this is the origin of the 20:1 Silver:Gold ratio in AD&D...
Let's ask the Wiktionary.
A coin, especially one valued at less than the principal unit of currency.
It seems to be quite an old term:
Middle English pece, from Anglo-Norman peece, peice et al. and Old French pece, piece et al., apparently from Late Latin *pettia, *pettium. Ultimate origin uncertain; perhaps from Transalpine Gaulish (compare Welsh peth, Breton pez (“thing”), Irish cuid (“part”)).
The most important historical precedent for parceling gold into "pieces" is Robert Louis Stevenson's Treasure Island (1881), an enormously popular work of fiction that was plundered and imitated by many authors in the following decades. While that work is more famous for the construction "pieces of eight," Treasure Island exemplifies usages like "pieces of gold" throughout to refer to pirate treasure. These precedents informed countless subsequent authors, especially authors of fantasy fiction, including Howard and Leiber. Conan, for example, knows of "men willing to sell their souls for a few gold pieces" in the 1930s. It is surely these usages that ended up informing the vocabulary of Dungeons & Dragons, as the authors of D&D cited these works specifically as influences.
I would say it is of historic origin.
Here in Sweden we had gold (and other valuable metal; copper was the most common) pieces that was simply weighed and that could be cut up if needed before we had coins.
At first it was simply a big hunk of metal later on it became "standard" sizes with stamps that guaranteed the weight and then after that came the coins (as we know them).