The Collaborative International Dictionary of English v.0.48:

Overstock \O"ver*stock`\, n.
   Stock in excess. --Tatler.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overstock \O`ver*stock"\, v. t. [imp. & p. p. Overstocked; p.
   pr. & vb. n. Overstocking.]
   To fill too full; to supply in excess; as, to overstock a
   market with goods, or a farm with cattle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overstock
    v 1: stock excessively [ant: understock]