Lycosa tarantula spiders take their name from the city of Taranto, where they are usually found.
The spider usually known as tarantula in turn takes its name from lycosa tarantula. I guess Italian immigrants in the Americas would call any big scary spider "Tarantola", and it stuck.
In turn, lycosa tarantula isn't really that poisonous, but it's big. It shares the habitat with the smaller, but more dangerous Latrodectus tredecimguttatus, and ends up taking the blame for its bites.