A tosher is someone who scavenges in the sewers, a sewer-hunter, especially in London during the Victorian era. The word tosher was also used to describe the thieves who stripped valuable copper from the hulls of ships moored along the Thames. The related slang term "tosh" referred to valuables thus collected, both are of unknown origin.
"Tosher" was also recorded from a slightly earlier period as undergraduates' slang for "an unattached or non-collegiate student at a university having residential colleges."
A similar-sounding term from the same period, "tosheroon" has been applied to a tosher in error, but denotes a piece of pre-decimal British currency: the crown.
A tosher in Victorian London is the profession of the title character in Dodger, a 2012 novel by Terry Pratchett.