The Collaborative International Dictionary of English v.0.48:

Impede \Im*pede"\, v. t. [imp. & p. p. Impeded; p. pr. & vb.
   n. Impeding.] [L. impedire, lit., to entangle the feet;
   pref. im- in + pes, pedis, foot. See Foot, and cf.
   Impeach.]
   To hinder; to stop in progress; to obstruct; as, to impede
   the advance of troops.
   [1913 Webster]

         Whatever hinders or impedes
         The action of the nobler will.           --Logfellow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

impede
    v 1: be a hindrance or obstacle to; "She is impeding the
         progress of our project" [syn: impede, hinder]
    2: block passage through; "obstruct the path" [syn: obstruct,
       obturate, impede, occlude, jam, block, close up]
       [ant: disengage, free]