Fa/tg/uy and armchair historian here. The word "bullet" can also refer to the ammunition for weapons like slings. As
>>24741758 notes, the word comes from the Latin "bulla," meaning "bubble," which became the French "boulet," meaning "small ball."
Even if we accept that the Pokémon world has no guns, it's a completely acceptable etymological path so long as weapons like slings still exist. Which, admittedly, we don't have solid confirmation on, but is reasonable to assume.
Of course, if such an etymology gave us "bullet seed" and "bullet punch" as deriving from "a projectile hurled at great speed and force," one would have to wonder why they're called Pokéballs and not Pokébullets, but weirder things have happened in language.
>>24743155Man, the derivation of "gun" is even weirder. It is generally accepted that the word came from a name given to a specific ballista in the fourteenth century (1300s), the Domina Gunilda. And "Gunilda" is believed to have come from the Norse name "Gunnhildr," which...basically means "war-battle."
So, it's the eqivalent of someone naming his AK-47 "Bertha" and then, decades later, having everyone refer to automatic weapons as "berths."
Again, though, since the word "gun" didn't just spring forth full grown from the head of Zeus to describe small arms, it's entirely possible that a similar derivation would have led to "water gun" without the handgonne ever having been invented.
>>24743279Cladistics, possibly. We do have multiple types of mouse Pokémon at this point, so it's possible that Pikachu was just the first. The scientific name for the humpback whale translates as "Big wings of New England," so it's not like cladistic terminology has to make sense.
>>24743959>duck-billed platypus>to contrast with all those species of non-duck-billed platypoda that we have running around 
