When Words Collide

The donkey has long been an image of slowness and dim-wittedness. Thus Michelangelo puts donkey ears on his critic Cesena, in the Last Judgment.

Indeed 'asinus' (the adjective, whence E. 'asinine') in Latin, could be used to mean not only donkeylike, but also stupid.

Or Euclid's pons asinorum: "The bridge of the asses," the proposition at which one moved into non-trivial proofs, and thus where the dunces would start to struggle.

Thus the original English word 'ass' (and later the masculine 'jackass'), from the Latin 'asinus', just referred to the animal: When used as an insult it was literally calling a person a donkey, with the implication of stupidity and dullness.

Meanwhile we have the Germanic 'arse' meaning the buttocks. Sometime near the beginning of modern English, it seems the 'r' dropped out, and 'arse' became 'ass'.

Etymonline gives us the history:

first attested 1860 in nautical slang, in popular use from 1930; chiefly U.S.; from dial. variant pronunciation of arse (q.v.). The loss of -r- before -s- attested in several other words (e.g. burst/bust, curse/cuss, horse/hoss, barse/bass). Indirect evidence of the change from arse to ass can be traced to 1785 (in euphemistic avoidance of ass "donkey" by polite speakers) and perhaps to Shakespeare, if Nick Bottom transformed into a donkey in "A Midsummer Night's Dream" (1594) is the word-play some think it is.

At this point confusion ensues. As noted, already in the 18th century polite company avoided 'ass' even when used with its older meaning.

In contemporary American usage, when one calls another an ass, it seems from my observation at least, that the intended significance is to identify the subject as a bottom. In fact, calling someone a donkey is sometimes used as a euphemistic play on words to call someone a butt, without the speaker realizing that he is in fact paraphrasing the original insult (so it is actually a very direct insult, according to the old use and neither a euphemism nor a play on words).

Thus the insult has remained largely unchanged, but its reference and signification has entirely changed. It's sort of like the invasion of the body snatcher. Only with words.