re the egocentric / geocentric 10-letter game.
I actually learned this word from Chi the last time it appeared in a game; since then I have heard it a couple of times - in films and tv series set in the 1920s / 1930s.
That would suggest that it is, at best, a bit old-fashioned. The sort of word I would expect to see in an E.M.Forster novel.
Common? Well, it was played by 16 from 299 players which would rather suggest it's not very common.