By rights, if the word were placed according to its meaning and not its spelling, it should lead the dictionary, shouldn’t it? I’ll have to dig out one of my bound dictionaries and get back to you.
However, I would expect to find it listed with any other collection on n-o-n-s* words, AND in the foreign language section in my American Heritage Dictionary of the English Language. Can’t confirm that right now, though.
Here, @LostInParadise. It’s pretty funny, given the meaning of non-sequitur. From @Call_Me_Jay‘s post, the first post in the thread. “Non seq“ui*tur. Etym: [L., it does not follow.] (Logic)”
But…you asked us all, and @Call_Me_Jay, in particular to specifically look it up on the 1913 Project Gutenberg link. Very few people have hard back dictionaries on hand any more, and certainly not one dating to 1913 (unless I’m misunderstanding something.)
Perhaps you should make a trip to your local library to research this.