Polari is a form of slang or cant historically used in Britain by some actors, circus and fairground showmen, professional wrestlers, merchant navy sailors, criminals and sex workers, and particularly among the gay subculture. There is some debate about its origins, but it can be traced to at least the 19th century and possibly as early as the 16th century. Polari has a long-standing connection with Punch and Judy street puppeteers, who traditionally used it to converse.

Thieves' cant is a cant, cryptolect, or argot which was formerly used by thieves, beggars, and hustlers of various kinds in Great Britain and to a lesser extent in other English-speaking countries. It is now mostly obsolete and used in literature and fantasy role-playing, although individual terms continue to be used in the criminal subcultures of Britain and the United States.