Variant of arse ; used ass in North America.
in culo alla balena
Contrary to the widespread belief of this being a euphemism, it arose as a pronunciation spelling of the older form arse still used in the UK, Australia, New Zealand, etc.
In the USA, "dropping Rs" non- rhotic pronunciation was common in prestige speech until the s, when the American Civil War shifted the country's centers of wealth and political power to areas with fewer cultural connections to the British elite.
See also these similar cases, culo of which retained both spellings with different meanings: From this stem, there are also Latvian reflexes with ak rather than as e. Compare Irish as.
Definition from Wiktionary, the bikini butt voyeur dictionary. See also: English Wikipedia has an article on: Printed for Tho. Printed by A.