bad job - balaclava - bandy-legged - barking, barking mad - barmy - Bath buns - Bath buns - bathing-costume - battlements - bauble - bedside cabinet - bell-pull - berk - besom - bin (binned, bin bag) - biscuit - bit keen - bit rich - black beetle - black pudding - bleeder - blighter - blimey - bloke - boater - bogey, bogies - bog-standard - Bonfire Night - bonnet - boot - bored of - bottom-of-the-table - bowler, bowler hat - Boxing Day - brew - budge up - budgie, budgerigar - bung - bunk, do a
He turned over the second page of the memo, saw how much longer it went on, and gave it up as a bad job (HBP1).
A woolly covering for the head and neck. The name comes from the site of a battle in the Crimean War; soldiers wore this kind of gear (NSOED).
See BARNABAS THE BARMY.
...he was also wearing the strange assortment of clothes so often chosen by inexperienced wizards trying to look like Muggles: in this case, a frock-coat and spats over a striped one-piece bathing costume (HBP10)
over the battlements and out of sight (HBP27)
A woman or girl, but this term is derogatory (though it can be used in a joking way). When used like this, it often appears in a phrase such as "old besom" (for an older woman) or "little besom" (for a young woman or girl). The word is also an old word for broom.
"Is it true that you shouted at Professor Umbridge?"
"Yes," said Harry.
"You called her a liar?"
"You told her He-Who-Must-Not-Be-Named is back?"
Professor McGonagall sat down behind her desk, watching Harry closely. Then she said, "Have a biscuit, Potter." (OP12)
A sausage-shaped dish made with blood and suet (animal fat) enclosed in a wrapper made from floury batter (NSOED).
"Bouillabaise," said Hermione.
"Bless you," said Ron.
"It's French," said Hermione, "I had it on holiday summer before last. It's very nice."
"I'll take your word for it," said Ron, helping himself to black pudding.
A stupid, unpleasant, or contemptible person or thing (NSOED).
"That treacherous old bleeder!" (DH22)
It's very much a slang term; someone trying to sound sophisticated/well-educated wouldn't use it (at least, if they knew what they were doing). It would sound very unusual for Percy, Hermione, or McGonagall to use it, and it's difficult to imagine Snape ever saying it.
"Blimey...you reckon it was this sign again?" (DH22)
"I can't - blimey!" (DH23)
"Blimey, a baby!" (DH25)
U.S.: guy, man. In the U.K., one sense of "guy" is that of a scarecrow-like effigy burnt on Bonfire Night, so saying that someone "looks [like] a guy" carries a different meaning than in the U.S.
a bit of a slap in the face for everyone who thought he was such a good bloke (DH20)
A flat-topped, hardened straw hat, with a brim. Often worn as part of the uniform of public schools. The name derives from the fact that the hats were worn by some University scholars, who would go boating on the river, but they became more widely popular as adult headgear in Edwardian times.
"flat straw hats called boaters" (PS3)
"We thought it was a bog-standard chicken until it started breathing fire." (OP7)
a.k.a. Guy Fawkes Night.
On 5th November every year, Britain commemorates the Gunpowder Plot, in which Guy (Guido) Fawkes and other extremist Catholics plotted (but failed) to blow up James I and his Parliament. People have firework parties or attend organized displays, and effigies of Guy Fawkes (known as "the guy") are burned on bonfires. The term bonfire is derived from 'bone fire' because, originally, bones were the primary material burnt.
"Viewers as far apart as Kent, Yorkshire and Dundee have been phoning in to tell me that instead of the rain I promised yesterday, they've had a downpour of shooting stars! Perhaps people have been celebrating Bonfire Night early..." (PS1)
Narrow jets of steam were issuing from under the bonnet (CS5)
If they won by less than three hundred points, they would come second to Ravenclaw; if they lost by a hundred points they would be third behind Hufflepuff and if they lost by more than a hundred, they would be in fourth place and nobody, Harry thought, would ever, ever let him forget that it had been he who had captained Gryffindor to their first bottom-of-the-table defeat in two centuries. (HBP24)
bowler, bowler hat
a small hat with a round top, used to be popular business wear in London (accompanied by umbrella)
Note that this is not strictly British usage.
The first weekday after Christmas day, so called because it used to be traditional to give Christmas-boxes (small presents or tips) on that day to people such as employees of firms providing regular services. (In modern usage the first day rather than the first weekday after Christmas Day is often referred to as Boxing Day instead.)
Everybody got up late on Boxing Day (GF24)
A small parrot-like bird kept as a pet, which in the U.S. is called a parakeet. See also Budgerigar Society.