The Collaborative International Dictionary of English v.0.48:

Shop \Shop\, v. i. [imp. & p. p. Shopped; p. pr. & vb. n.
   Shopping.]
   To visit shops for the purpose of purchasing goods.
   [1913 Webster]

         He was engaged with his mother and some ladies to go
         shopping.                                --Byron.
   [1913 Webster]