Q From David Sutton in the UK: What is the gaff in blow the gaff?
A That’s not so common a British slang phrase these days, though it’s still about:
Before Danny blew the gaff, all we knew of the Bank’s debates about monetary policy was gleaned from the dull, jargon-ridden tones of the monthly minutes and the quarterly inflation report.
Evening Standard (London), 14 Dec. 2010.
Blow the gaff starts to appear early in the nineteenth century as criminal slang. It isn’t easy to find an origin — a lot of dictionaries don’t even try — because the matter is clouded by the fog of ages and the poor state of recording of early slang. There are also all sorts of meanings for gaff recorded down the centuries, which has added to our difficulties.
The standard English sense is of a hooked stick or barbed spear used for landing fish, at one time transferred to a horse-rider’s or fighting cock’s spur. This is from the Provençal word gaf for a boat-hook. In French this took on the figurative sense of a blunder, perhaps because the emotional effect is like being gaffed, and it’s the origin of the standard English gaffe for an embarrassing remark or blunder. In the middle of the nineteenth century it was also the source of another sense:
The gaff is a ring worn on the fore-finger of the dealer. It has a sharp point on the inner side, and the gambler, when dealing from a two-card box, can deal out the card he chooses.
Vocabulum: or, The Rogue’s Lexicon, by George Washington Matsell, 1859. Matsell was Chief of Police in New York City and a part-owner of the National Police Gazette. This extraordinary guide to criminal slang was compiled for his colleagues.
Together with the English dialect gaff for loud and coarse talk, or the same Scots word gaff which meant to talk loudly and merrily, this gave rise at the beginning of the twentieth century to an American slang sense that referred to severe criticism, treatment, or hardship (as in stand the gaff or give the gaff).
Then there’s the British slang meaning of gaff for the place where one lives (“come round my gaff for a coffee”), which is almost certainly derived from the use of gaff in the eighteenth-century to mean a fair, and later a cheap music-hall or theatre (as in the infamous penny gaff) and which probably comes from the Romany gav for a town, especially a market town.
But none of these is the immediate source for blow the gaff. We have to go back to the eighteenth century, when there was another version of the expression, to blow the gab, criminal slang meaning to reveal a secret or to betray a confederate; gab means conversation or speech (as in gift of the gab) and blow itself had earlier had the slang sense of informing on confederates:
As for that, says Will, I cou’d Sell it well enough, if I had it, but I must not be seen any where among my old Acquaintance; for I am blown, and they will all betray me.
History of Colonel Jack, by Daniel Defoe, 1723.
This is a famous early appearance of the full expression:
I, Crank Cuffin, swear to be
True to this fraternity;
That I will in all obey
Rule and order of the lay.
Never blow the gab or squeak;
Never snitch to bum or beak.
The Oath of the Canting Crew, taken from The Life of Bampfylde Moore Carew, by Robert Goadby, 1749. Crank Cuffin was a generic term for a rogue; squeak and snitch also refer to becoming an informer; a bum was a bailiff, a lowly law-enforcement officer (his name was an abbreviation of bum-bailiff, one who was close behind you in pursuit); and a beak was a magistrate.
We may guess that blow the gab changed into blow the gaff under the influence of one of the senses of gaff. We don't know for sure when this happened but the earliest known example of the expression is this:
A person having any secret in his possession, or a knowledge of anything injurious to another, when at least induced from revenge, or other motive, to tell it openly to the world and expose him publicly, is then said to have blown the gaff upon him.
A Vocabulary of the Flash Language, by James Hardy Vaux, 1812. Vaux was then a transported criminal in New South Wales, Australia. Flash is an old term referring to thieves, prostitutes, or the underworld.
This is an early example of the expression from outside the criminal world:
One of the French officers, after he was taken prisoner, axed me how we had managed to get the gun up there but I wasn’t going to blow the gaff, so I told him as a great secret, that we got it up with a kite; upon which he opened all his eyes, and crying “Sacre bleu!” walked away, believing all I said was true.
Peter Simple, by Frederick Marryat, 1833. Axed here is a dialectal form of asked.