Some words shared by all English speakers are spelled differently by Americans and Britons. Many of these are American "simplification" of the original spellings, often due to Noah Webster. In some cases, the American versions have found their way across the Atlantic and become common British usage as well, for example program (in the computing sense).
The differences most likely to create confusion are in the use of different words for concepts. Most of these are for modern concepts where new words were coined independently, or else the terms are slang or vulgar. Regional variations even within the US or the UK can create the same problems.
It should also be noted that most American words can be freely interchanged with their British versions within the United Kingdom without leading to confusion. It tends to be only when the situation is reversed that problems occur. However, there are some exceptions, such as dumpster and stroller (in the sense of pushchair) which are unlikely to be understood by most speakers of British English.
British American
aerial antenna?
arse ass (buttocks)
barrister lawyer (distinction only in British law)
bollocks balls (testicles) (interchangeable in British English)
bloody damn (e.g., This bloody car won't start.)
bonnet (of a car) hood
boot (of a car) trunk
candy floss [cotton candy]?
concession discount?
crisps chips? (e.g., potato or corn)
current account [checking account]?
engaged tone [busy signal]?
fairy cake cupcake?
indicator [turn signal]?
laundrette laundromat
lorry truck? (interchangeable in British English)
maths math
MD (managing director) CEO (Chief Executive Officer)
mobile (phone) cell phone
nappy diaper?
paraffin kerosene
petrol gasoline
pram [baby carriage]?
pudding dessert (interchangeable in British English)
randy horny? (interchangeable in British English)
ring someone call someone (interchangeable in British English)
Heath Robinson Rube Goldberg
settee couch? (interchangeable in British English)
shag fuck? (interchangeable in British English)
(shag is a kind of carpet and a dance in American English)
snogging kissing / "making out"
spanner wrench
solicitor lawyer (distinction only in British law)
sticking plaster Band-Aid?
American British
ass arse
busy signal engaged tone
checking account current account
cookie biscuit
cotton candy candy floss
cupcake fairy cake
diner cafe
dumpster skip
french fries chips
gasoline petrol
math maths
stroller pram
turn signal indicator
Word American equivalent of British equivalent of
exclusively British exclusively American
meaning meaning
bum butt? (buttocks) hobo, homeless person
cafe diner? French cafe
chemist pharmacist, pharmacy
chips french fries crisps?
biscuit cracker or cookie
bonnet hood? (of a car)
boot trunk? (of a car)
dummy pacifier
fag cigarette? queer?
fanny pussy? (vagina) bum (not obscene)
flat apartment?
lift elevator
limited (Ltd) incorporated?
lounge [living room]?
pavement sidewalk? the road surface
pissed drunk angry
rubber eraser?
rubbish garbage? / trash
silencer muffler?
skip dumpster?
tap faucet?
torch flashlight?
tube subway
underground subway
valve tube, or vacuum tube
The name of the letter Z is pronounced zed in British English as opposed to zee in American English, though the words are rarely spelled out in either. Some greek letters, such as theta and beta, are also pronounced differently.