"You say po-tay-to, I say po-tah-to"
The United Kingdom may be an English speaking country, but some words still need translating!
Bin/Rubbish: The British word for "trash-can" or "garbage"
Biscuit: Cookies! "Tea and biscuits"
Chips: Nope, if you are offered "chips" you will not be getting tortillas or Lays. Chips are what the British call "french fries". Potato chips would be referred to as "crisps"
Fanny: You may need to find another word for "fanny -pack" as in England the word "fanny" is a slang for lady bits!
Fancy dress: If you're invited to a "fancy-dress" party they mean a "costume" party
Holiday: If your colleague asks you how your "holiday" was, he/she is referring to your "vacation"
Love: A bit like "hun" or "dear", "love" is an informal term of endearment that you will likely be called at some point by the local barmaid, shop attendant, or neighbour.
Mobile: When the British talk about their "mobile", they are referring to their cell-phone
Pants: Unlike in the States, pants do not mean trousers/fabric that covers your legs. Pants are your underpants!
Posh: Posh means "fancy" or "high-end"
Rubber: If someone asks you for a rubber he or she is not referring to a condom (although this thought always crosses my mind!). Rubber is an"eraser"
Tea: This could be referring to a cup of tea, but it also could be in reference to an early dinner! "Would you like to come around for tea around 5 pm?
Torch: If someone asks for a torch he or she does't mean a stick with fire. A torch is a flashlight.
Trainers: Forget about ever referring to your gym shoes as "sneakers" again! Sneakers are trainers in the U.K.
University: What Americans would call "college". However, it is good to note that the British also have a schooling period called college, but it comes before university (about age 16).
Grammarcheck has a great list with nice info-graphics and additional spelling differences.