As
defined above and below, a riddle is either a
conundrum, or a board with holes in it.
I found THIS trio of definitions to be entertaining.
Something can be riddled with holes, either in an arrangement or at random.
A board with holes is used to riddle a bottle of champagne. The necks of the bottles are inserted in the holes downward, so that any sediment (also called must) in the wine will fall out of solution. The bottles are then briefly opened and the sediment removed.
A riddle is a sort of word puzzle, where the answer falls out of solution.