a warning cry given before throwing dirty water from a window
Those living on the top floor of tenements would dispose of their urine by emptyingthe container into the street out of an open window, shouting 'Gardyloo!' to warnanyone below.
gardyloo in American English
(ˌgɑrdiˈlu)
interjection
Obsolete
in Edinburgh, used as a warning to people below that slops were about to be thrown from a window into the street