GAME - NAME A RHOMBOHEDRON

A brief survey of the most discussed "articles" during the past week discloses more than a dozen "games" asking participants to name a . . . (whatever).  These games are neither articles nor are the responses "comments".  They are merely a means by which those who are dumber than a head of lettuce can while away their useless lives.

Some of the so-called games found in the top 75 "most discussed articles" include:
Name an actor, a beer, a flower, a gift, a movie, a perfume, a sign,  a song, a sound, a tv show and a word.  All very challenging, I'm sure - especially if you're dumber than a head of lettuce, and all accumulating much-coveted points for the author.  Personally I don't need no stinkin' points.

For those of you out there who are decidedly smarter than a head of lettuce, I have designed a game just for you.  Seeing as how it is somewhat more challenging than the average game I am not expecting anywhere near the 100+ comments the others garner.  If I get three comments I'll be quite happy.

So here is your challenge, if you care to accept it:  name a rhombohedron.  Good luck.