The Collaborative International Dictionary of English v.0.48:

Impound \Im*pound"\, v. t. [imp. & p. p. Impounded; p. pr. &
   vb. n. Impounding.]
   To shut up or place in an inclosure called a pound; hence, to
   hold in the custody of some authority such as police or a
   court; as, to impound stray cattle; to impound an illegally
   parked car; to impound a document for safe keeping.
   [1913 Webster +PJC]

         But taken and impounded as a stray,
         The king of Scots.                       --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

impounding
    n 1: placing private property in the custody of an officer of
         the law [syn: impoundment, impounding, internment,
         poundage]