The crapper
What's the meaning of the phrase 'The crapper'?
The lavatory.
What's the origin of the phrase 'The crapper'?
Popular wisdom attributes the derivation of this slang term for lavatory to Thomas Crapper (1836 - 1904), the supposed inventor of the flushing toilet. Unfortunately, Thomas Crapper didn't invent the flushing toilet. The first device recognisable as a flushing lavatory was invented by the English Tudor courtier Sir John Harington.

Nevertheless, Crapper is the name that people remember. He was certainly well-known in his day as a sanitary engineer. He had a thriving plumbing business and was sanitary engineer for several members of the royal family.

"Where's the plant, cully?"... "Fenced, in a dunniken."... "What? Fenced in a crapping ken?"
Swell's Night Guide was a magazine that circulated amongst the unruly elements of London society. By 'crapping ken', the author meant 'outside privy'. Note that the alternative name 'dunniken' is still with us in the form of 'dunny', which is an Australian slang term for lavatory.
There are older Dutch and German words 'krappe/krape' and an English version 'crappe' that could have been the source of Crapper's name, but none of these actually mean defecate or excrement.
Thomas Crapper didn't begin work as a sanitary engineer until 1861, several years after 'crapping' was clearly known as a slang term for defecating, so his name couldn't have been the source of the term. However, the coincidence of the name of the foremost Victorian sanitary engineer and the existing expression must have given an impetus to 'crap' being more widely taken up and hence staying with into the 21st century.
