We borrowed the word toxic from French toxique in the late seventeenth century. Toxique comes from Latin toxicus, which meant "poisoned", not unlike today's definition. This in turn comes from Ancient Greek toxikon, which had the very specific meaning of "poison meant to be used on arrows". There was actually a more ubiquitous word for "poison" in general, ion, but the io- sound was considered "too weak" so, for scientific purposes, toxikon was repurposed instead. Now, the word toxikon can be conjugated to toxikos, meaning "of or pertaining to bows", from toxon, "bow" (you can see here the metonymic shift, through association of poison on the bows). Finding the etymon of taxon is difficult, as nothing is confirmed about it. Linguists think that there is a connection to the Latin word taxus, which had a definition of "javelin", and that both words either come from a Scythian origin or the Iranian word taxsa, meaning "bow".
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.