Khazi
Origin
Possibly from Italian casa ("house"), via 1870s Cockney word carsey,
A dictionary of slang and unconventional English, by Eric Partridge et. al., 8th edition, 2002, p. 185
and possibly via Polari and Sabir
Alan D. Corré, "Polari Words from Lingua Franca" in: A Glossary of Lingua Franca, 5th Edition, 2005
Or a contraction of "Gazebo"
Possibly from an African language (Zulu or Swahili are often cited) word "M'khazi" meaning a latrine.
Usage notes
Particularly used in "down the khazi".
Khazi is now most commonly used in Liverpool, away from its cockney slang roots.
"Why Do We Say?" (1987) by Nigel Rees