Well, it does look like you have their Word of the Day email; plenipotentiary was featured as a Word of the Day a few days ago (if memory serves).
Granted, I was going to submit it myself, hoping nobody would notice it, but...
I only know Word Crazy from Merriam-Webster; did they make other such games? (Word Crazy was for computers, and was released several years ago; 1995 or 1996 perhaps)
Arabesque will be my not so daily contribution. It is a noun, pronounced more or less like "arabesk". Its meanings are as follow:
1) A ballet position (no, I will *not* do it myself)
2) An ornate musical composition, especially for piano
3) An intricate or elaborate design or pattern, that may include floral or geometric figures.