From 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]