Invitation to post-hoc reasoning?

I’m running through the morning vocabulary drill, and I note that the definition for luego is that is an adverb meaning “later (on), afterwards, then, next” and it’s also a conjunction meaning “therefore”.

It strikes me as dangerous to use the same word for “after” and “therefore”—in fact, it strikes me as a glaring example of (and invitation to) post-hoc reasoning. Post hoc (full expression: post hoc ergo propter hoc: “after this therefore because of this”) leads to all sorts of errors: “X happened, and then Y happened, so Y must have been caused by X” is not a reliable formula. And to use the same word for “afterwards” and “therefore” not only invites such fallacies, it practically demands them.

Perhaps it is only a lexicographer’s error. When I look up (using the same on-line dictionary WordReference.com) the meaning in Spanish of the English word “therefore”, I see that apparently Spanish lacks a word meaning therefore (Latin: ergo). They do offer a couple of workarounds: “por tanto”, “por eso”. But no actual word for therefore—except, of course, for “afterwards”.

I am dissatisfied.