Quadraped, equine family with long ears :- donkey
To be compared to a donkey:- ignorant and stupid, an insult.
"You stupid ass!"
A popular but childish corruption of the word:- arse
which came about by the popularization of malapropisms and poor diction in uneducated American media commentary and colloquial speech normally associated with thugs, gangsters and lower working class. (TV interviews of simple folk.) C1950s
Children will mispronounce words and confuse them unless corrected by adults. If the adults know no better ( foreign language use) then the word is accepted into the adult language without challenge and becomes an indicator word for ignorance. ( A lack of knowledge).
Moreover, ass is a product of censorship in America to avoid the use of the word "arse" on TV. 'Ass' was used in its place to circumvent the censor C1950s. (It was ok to call someone an 'ass' but not an 'arse') Americans still use the word to replace arse but are confused as to its origin and meaning.
The confusion of ass / arse, continues from the lack of phonics taught in American infants classes and the continuing lack of eloquence in the media and some of the adult population.
The words are not the same nor do they sound the same, nor do they have a similar derivation.
When ass is used in place of arse, it acts as an education and class indicator and deflects the listener to ridicule the intellect or background of the speaker, in most cases silently.The intended insult, "you ass hole", or description is lost unless, of course it is used on someone from the same background who is equally ignorant.