Source : Webster's Revised Unabridged Dictionary (1913)

Muggins \Mug"gins\, n. [Etym. unknown.]
   1. A game of dominoes in which the object is to make the sum
      of the two ends of the line some multiple of five.

   2. A game at cards which depends upon building in suits or
      matching exposed cards, the object being to get rid of
      one's cards.

Muggins \Mug"gins\, v. t.
   In certain games, to score against, or take an advantage over
   (an opponent), as for an error, announcing the act by saying
   ``muggins.''

Source : WordNet®

muggins
     n : a person who lacks good judgment [syn: {fool}, {sap}, {saphead},
          {tomfool}]