stumper(n = noun.communication) poser, sticker, toughie - a particularly difficult or baffling question or problem;
is a kind of problem
Derived form verb stump₁

1.  One who stumps. [1913 Webster]

2.  A boastful person. [1913 Webster]

3.  A puzzling or incredible story. [1913 Webster]

stumper, n. colloq.
1 a puzzling question.
2 a wicket-keeper.