Actually, "radical" doesn't mean "extreme", it comes from *radishes*, the anarchist's favorite tuber
@abgd radical stems from the root "radix" (root). So basically radical originally meant "fundamentalist".
@tzafrir Umm yeah, this is a joke, taking off on the real explanation which radicals often have to make.
But as it were, "radish" is actually also a cognate of "radix" (since it's a root vegetable, aka tuber), so the joke is true too. :P