I love that in Westron there is a specific name for this game.

• 05.077 that the riddle-game was sacred

The sub-entry for this word is a two-word word, with a space not a hyphen, except in one example … from Tolkien (Fellowship of the Ring).  I’m giving him the credit for the hyphenated spelling.

“riddle, n.1.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/165631. Accessed 19 September 2017.