Normally, I’d know what the word means, but in reading stuff for a philosophy class, it was obvious that the usual meaning wasn’t what was being used. So, I went a-Googlin’. It turned out to refer to a problem in inductive inference, wherein the color “grue” is used to describe items which are green before a given time, but will be blue after a certain time.
I don’t think there’s a semester where I’m not scratching my head over the words used in at least one philosophical reading. I was encouraged to just jump into senior-level courses without having intro courses, and I’m holding up well, but the field has a well-developed vocabulary that is baffling to outsiders like me.