The Collaborative International Dictionary of English v.0.48:

Shoplifter \Shop"lift`er\, n. [Shop + lift. See Lift to
   steal.]
   One who steals anything in a shop, or takes goods privately
   from a shop; one who, under pretense of buying goods, takes
   occasion to steal.
   [1913 Webster]

WordNet (r) 3.0 (2006):

shoplifter
    n 1: a thief who steals goods that are in a store [syn:
         booster, shoplifter, lifter]