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:
Piece
Piece is, according to several dictionaries, a common term for coins in general, of whatever denomination is specified. The quote below is excerpted from the etymology online page:
piece
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.
Commentary
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...
Best Answer
The term itself is made up and merely descriptive, and was probably derived from a recent (2010) Penny Arcade strip.
Its reputation as a campaign-ender predates this specific name (and definitely predates 2010), having been recognised as a source of chaos that strains a campaign at the seams as far back as AD&D.
I say the name is merely descriptive: when the Deck appears in a campaign, its effects are often disruptive to a degree that the campaign cannot continue as it was. Since D&D campaigns today are often more story-based than when the Deck was first published, its reputation as a campaign-ender has only grown since then. The Penny Arcade comic emphasises the story as the Deck's potential point of disruption. (Non-story-based campaigns are less vulnerable to disruptions in general, even TPKs. Such a campaign will certainly change direction significantly due a disruption such as a TPK or the effects of the Deck, but won't necessarily end due to it. In practice, even non-story-based campaigns have the potential to be disrupted though, as emerging event lines that the group have invested in may crash and burn — campaign vulnerability to the Deck is a spectrum.)