Kex is a letter, OF COURSE. The long elusive 27th letter. Most often thought of as a cross between K and X. No one can quite draw a picture of it though.
Eleventeen is that tricky number after twelve, but can also come four more times before twenty. Perhaps it's like Elevensies to a Hobbit?
Now, a Hemptagon is something like a hexagon and something like an octagon. But not.
When we figure these things out, we'll let you know.