Words don’t just pop out of thin air. They all come from previous language and builds up.
The word riddle can be traced to all the way back to its PIE root “krei-” which means to sieve. In Old English the word “hriddel” is the direct root of riddle. This word meant “Coarse sieve.” Riddles can be related to sieves in that you start with all possibilities but you use the clues in the riddle to slowly sieve away all of the incorrect answers until you arrive upon the correct one.
For some great hriddels visit Good Riddles Now’s good riddles section.