New Words For Old

Stumbled upon the word caliginous over the weekend, in some work I was marking. I couldn't recall coming across it before, but it looked sort of meaningful in context and seemed used with assurance - as opposed to being something misheard, or a more common term being mangled. I looked it up and it turned out to mean something along the lines of dark or dim or misty. It has a respectable Latin origin and at least one on-line source marks it as archaic, but the Ngram Viewer indicates quite a steep increase in use since 2000, with the lowest usage belonging to the 1940s. Must ask the student where they got it from.
 
I think this is the first time I've ever failed to recognise a word used in work I've been marking, apart from ridiculous academic jargon, that is. It was a salutary experience. I suppose people with quite narrow vocabularies experience what I felt all the time: a sort of mild irritation at being excluded from the discourse, and a deeper sense of inadequacy at being not quite good enough to grasp what was in front of me.

I'm not too sure I want to commit the word to memory, or active use though. It seems too arcane. Mind you, it features in The Wizard of Oz, it seems, used of the Tin Man. I did wonder if Milton had jammed it somewhere into his great epic, but Johnson's Dictionary doesn't attribute it to our Puritan poet, so I figure not.