Source : Webster's Revised Unabridged Dictionary (1913)

Poser \Pos"er\, n.
   One who, or that which, puzzles; a difficult or inexplicable
   question or fact. --Bacon.

Source : WordNet®

poser
     n 1: a person who habitually pretends to be something he is not
          [syn: {poseur}]
     2: a person who poses for a photographer or painter or
        sculptor; "the president didn't have time to be a model so
        the artist worked from photos" [syn: {model}]
     3: a particularly difficult or baffling question or problem
        [syn: {stumper}, {toughie}, {sticker}]