The Collaborative International Dictionary of English v.0.48:

Murphy \Mur"phy\, n.
   A potato. [Humorous] --Thackeray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

murphy
    n 1: an edible tuber native to South America; a staple food of
         Ireland [syn: potato, white potato, Irish potato,
         murphy, spud, tater]