the.com/ass

means A body part, a fool, or a donkey — and increasingly, thanks to the internet, the entirety of an adjective.

from Two words collided into one spelling. The donkey sense traces back to Old English 'assa', itself borrowed from Latin 'asinus' — the source of 'asinine' too. The buttocks sense comes from a different root, 'arse', which lost its 'r' in American pronunciation and merged on the page with the donkey word, even though the two started out as strangers. The donkey's reputation for stubbornness and stupidity helped the insult sense ('don't be an ass') bridge the two meanings so thoroughly that most speakers now feel they were always one word.