For example, boondocks (rural area or wilderness) or duplex (a two-family dwelling or an apartment on two floors).
The most confusing words are those which are used in both languages, but have slightly different meaning.

American means what Brit calls: Brit means what American calls:
bill banknote check
chips crisps french fries
mad angry crazy
pants trousers underpants
pavement road surface sidewalk
purse handbag wallet
rubber condom eraser
subway underground railway underpass
vest waistcoat undershirt

Despite all the differences British and American people understand each other without big complications. After all both speak one language, English.