The Collaborative International Dictionary of English v.0.48:

Tamp \Tamp\, v. t. [imp. & p. p. Tamped; p. pr. & vb. n.
   Tamping.] [Cf. F. tamponner to plug or stop. See
   Tampion.]
   1. In blasting, to plug up with clay, earth, dry sand, sod,
      or other material, as a hole bored in a rock, in order to
      prevent the force of the explosion from being misdirected.
      [1913 Webster]

   2. To drive in or down by frequent gentle strokes; as, to
      tamp earth so as to make a smooth place.
      [1913 Webster]