When traveling to a foreign country, it's helpful to at least know how to ask where to find the bathroom in the native language. But even in English-speaking countries, you have a lot of options for how to ask for the water closet. Some are more polite than others, but the meanings are clear.
Lavatory
This has nothing to do with a volcano — "lavatory" comes from the Latin lava, which means "to wash." A lavatory was originally something in which to wash, such as a bathing pool. Around the 17th century, it turned into a room with washing facilities, and in the 19th century, it adopted its current meaning. A lavatory usually has a toilet and washbasin, but not a full shower or bathtub.
Loo
This one is quintessentially British. Rumor has it that an early toilet manufacturer named its model the Waterloo, after the infamous battle. Now you can "visit the loo" all across the United Kingdom.
Bog
Another British creation, "bog" used to be slang for an open pit used to store human waste. There are not too many of those around these days, but "bog" is still slang referring to the toilet. The term has even been expanded to "bogroll," which refers to toilet paper.
John or Jakes
"John" is an American term for the toilet, although it's thought to have originated from a British man, Sir John Harington. Sir John Harington was a 16th-century writer, but his real claim to fame is creating the first flushing toilet (using a flush valve to release water to rinse out the bowl). His name for the toilet was "Ajax," which likely gives us the British slang for toilet, "jakes." Queen Elizabeth was an on-again/off-again fan of the controversial writer, nicknaming him her "saucy Godson."
Crapper
Americans love to borrow terms from the British. Thomas Crapper was an 18th-century British plumber who founded the successful sanitary equipment outfit Crapper and Co. No, really, this is a true story. Toilet lids across the U.K. were stamped with "The Venerable Thomas Crapper & Company," tickling the funny bone of American GIs during World War II. They brought home the somewhat impolite term "crapper."
Dunny
In Australia and New Zealand, "dunny" was used for the outside toilet or outhouse. It came from the British word "dunnekin," with "dung" or "dunne" meaning waste.
Comfort Room
Here's a polite euphemism from Filipino English. If you are in or around the Philippines and see “CR” on a door, now you know what to expect.
Privy
Used in both Britain and America, this term originated in Scotland as an alternate word for "private." Now it’s used in America when referring to outhouses.
Khazi or Karzy
This word was borrowed in the 1960s from the Italian word "casa" for house. These variations are now almost exclusively used in Liverpool.
Pissoir
A French word, "pissoir" is used to refer to public urinals and comes from the word to urinate: pisser. Yes, it’s likely the unsavory English term came from this, too.