Thanks for the clarification, Sir Doris. But what about the “mar”? Is it like “mare” (female horse" or “mar” (to mark or stain).
How about the British use of do to refer to a party or event? My British in-laws referred to the reception they threw for us as “the evening do.” I have also heard them refer to a bachelorette party as a “hen do.”
This morning, my husband said something like “We might need to hire a van to move house” whereas an American would probably say “We might need to rent a van to move (or to move our things).” According to him, Britons rent places to dwell, but other things (tools, cars, taxis) are all hired.
Sir Doris, Americans use “I’ll catch up with you later” or “I’ll get you caught up” in that second sense, too: that of becoming updated on past events.
I think “pretty good” in Americanese is a good equivalent for “quite good” in Britspeak.
And yes, “mates” for “friends” feels substandard in the way I’ve heard it used. I almost didn’t mention it, because we could go on for months about the differences in substandard words and slang. 
FISH
Or as the P.G. Wodehouse character Uncle Fred, fifth Earl of good old Ickenham put it, “what is better than an eel? For jellying purposes, I mean.”
Haven’t seen anyone mention this one:
American ‘booger’ = UK "bogey’ (or ‘snot’)
Sorry.
“Marrow” rhymes with “narrow” … it’s that simple.
Julie
Indeed, although pumpkins seem to have rather superseded marrows in the giant vegetable competitions now, probably because the maximum size of a pumpkin is so much more spectacular.
Forgot to add …
Americans say “in back of” the house whereas Brits say “behind” the house. Although we all say “in front of” …
Americans say “I could care less” (never understood that one!) whereas Brits say “I couldn’t care less”.
American “purse” = British “handbag/bag”
American “pocketbook” = British “purse” (female)/ “wallet” (male)
American “pantyhose” = British “tights”.
Julie
I’ve seen a few people allude to the jam/jelly thing in this thread, but i’m given to understand that the terms ‘jam’ and ‘jelly’ mean exactly the same thing on both sides of the Atlantic, the only difference being the popularity of preference one vs the other.
Also, I mentioned ‘milk chocolate’ in another thread once and this seemed to be misunderstood by Americans as something to drink; I’m not sure whether that was just a one off, but:
‘Milk chocolate’ = ordinary (solid) chocolate that includes milk solids.
‘Plain chocolate’ = dark chocolate that does not include any milk solids.
‘candy’ is not a common word here (although usage is on the increase) and traditionally the word would have been reserved specifically to describe hard sugar confectionery.
I don’t think many Americans use the term “pocketbook” these days, except in a figurative or symbolic sense, e.g. “that extra sales tax really hits me in the pocketbook”. For the actual physical accessory we’re more likely to say wallet or purse.
Does anyone else say ‘turnip’ instead of ‘rutabaga’? Thanks for this thread… I now know what a ‘swede’ is. Confused the hell out of me when I read Watership Down.
Sunspace, turnips and rutabagas are not exactly the same, although they are in the same family (genus brassica). Rutabagas are much larger and have smooth leaves, compared to the prickly leaves of the turnip. Turnips are usually white-fleshed, rutabagas usually yellow-fleshed.
Oooh, I thought of one:
American= “Real Estate” & “Real Estate Agent” (or (I think)“Realtor”)
British = “Property” & “Estate Agent”
With regard to my comment on the American Subjunctive, I see that it was covered in some detail in this thread.
I’ve thought of another very basic difference. Why do Americans say they live, or that a business is located, on a street while Brits say in the street? In Americanese, to be in the street means literally in the middle of the street, where you would be in danger of being run down by a car. But Brits will say they live in a street. Is the word street considered to include the asphalt, sidewalks, and the houses as a group concept?
While vacationing in London, I was surprised to hear someone actually say “cheerio” to me; I didn’t think that was still used. Of course here in the U.S. a “cheerio” is a little O-shaped cereal.
But my favorite is guy = bloke. In the U.S. it’s becomd acceptable for “guy” to include females when used collectively, as in “you guys,” but in London I heard “bloke” only referring to males.
Yes, “the street” is generally taken to mean the whole thing, including buildings.
The only instance I can think of where we use “on” is as in “she’s on the streets”, ie a hooker. 
Julie
In the UK the edge of the pavement ( sidewalk ) is referred to as the Kerb. We still use the word “curb” but meanimg to put a stop to something.
Also a ( UK ) rubbish skip is a (US ) dumpster
Oddly enough, the work “bloke” was used in New York City slang of the 19th century, as were British style rhyming expressions, today practically unknown in the U.S. I read of this in Alvin Harlow’s Old Bowery Days as well as Herbert Asbury’s Gangs Of New York. As a result of that, I doubt that these expressions were used much throughout all milieus and social classes, but they were definitely used by someone.
cheerio is generally what old folk say
bloke is a real mans man
bird is his woman (bitch)
Aha! I think I have the answer to Davebear’s pronunciation of Robin Hood. It’s the famous old song, you know, the one that goes:
Robin hood, Robin Hood, riding through the glen
Robin Hood, Robin Hood, with his band of men
Feared by the bad, loved by the good
Robin Hood
Robin Hood
Robin Hood
In which the emphasis is always on ‘Robin,’ not ‘Hood.’