back slang
Definition - A type of Cockney slang in which words are pronounced as if spelled backwards.

Example -
The yob's spinsrap
(Translation: The boy's parsnips.)

Etymology -
Some claim that the phenomenon originated in 19th-century Cockney London among market sellers, such as butchers, but I haven't found any sources other than the OED citation below that back this up. If anybody has any further info, please let me know.

Oxford English Dictionary -
The term's first citation is from 1860 (in Modern Slang, 256). Its first quoted citation is from 1862 (Wheatley):
"Back Slang … is formed by the costermongers upon anagrammatical principles; thus look is cool."
(Wheatley Anagrams, 141)

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