Essential Americanisms which Brits need to know, such as American English and snap fastener

Angela Lansbury with the flag, of Great Britain and Northern Ireland, called the Union Jack. Photo by Angela Lansbury.

The first thing I discovered when I looked up Americanism in Wikipedia is that Americanism to Americans is the term for a political movement. What I call Americanism is what Wikipedia calls American Language.  Here are some other words which are sometimes called 'false friends'.

American English - British English

American English - Americanism

Americanism + political party's promotion of US first

closet - wardrobe

eraser - rubber

Jello (brand name) - jelly

Kleenex - tissues, paper hankies

mix, mixed breed, mutt - mongrel

pants - trousers

popsicle - ice lolly

real estate - property

underpants - pants

snap fastener / metal snap - press stud

British English - American English

Americanism - American English

condom/Durex (brand name) - rubber

ice lolly - popsicle

jelly - Jello

mongrel - mutt, mix, mixed breed

Mom and Pop store - family owned corner shop

pants - underpants

paper hankies/tissues - Kleenex (brand)

parking lot - car park

press stud - snap fastener

property - real estate

rubber - eraser

trousers - pants

wardrobe - closet