Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

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