Someone who was feisty in a Middle English context would find it hard to be feisty today. It’s actually quite interesting what happened: we got our current definition in 1896, from feist, which meant “a small dog”. It’s not too hard to draw a parallel to “spunkiness”, for small dogs are unusually manic for their size, and feisty in particular alludes to this one enthusiastic dog breed. But then again, many dogs smell, so it’s also not a surprise when we trace feist to a word meaning “stink”. And you know what stinks? Farts. So, in Middle English, feist meant “fart”. Through Old English, this goes all the way back to fistiz (also “fart”), which probably traces to a Proto-Indo-European word sounding like perd and still meaning “fart”. Of course, the transitions were more nuanced than I'm describing here; for periods in between meanings of feist people were using it for more than one definition, and things generally got confusing.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.