Other forms: puzzlers
A puzzler is a confusing or tricky problem. The mystery of why you always lose your car keys can be described as a puzzler.
You might be sure you'll ace your math test until you get to the final question, a complete puzzler that you can't figure out how to solve. Other kinds of puzzlers could be the complicated plot of a novel you're reading or what the secret ingredient is in your dad's brownie recipe. The noun puzzler has been around since the mid-1600s, from puzzle, "bewilder or confound."