As far as I can tell, “parlous” and “perilous” mean exactly the same thing, except that almost no one knows what “parlous” means. Which means, to me, that anyone using the word “parlous” is intentionally trying to point out that they are more well read than I am, which makes them an elitist snob. If I’m wrong, please let me know, but, until someone straightens me out, I am going to point and laugh at anyone using the word “parlous”.
I guess I’m an elitist snob. I like the word “parlous.” And it actually works quite well in a series my sister and I are writing together. Of course, I won’t put it in every book. There’s only one word that has to be somewhere in every book I write–except kids’ picture books–and that word is borborygmus.