The Collaborative International Dictionary of English v.0.48:

Tap \Tap\, v. t. [imp. & p. p. Tapped; p. pr. & vb. n.
   Tapping.] [F. taper to strike; of Teutonic origin; cf.
   dial. G. tapp, tapps, a blow, tappe a paw, fist, G. tappen to
   grope.]
   1. To strike with a slight or gentle blow; to touch gently;
      to rap lightly; to pat; as, to tap one with the hand or a
      cane.
      [1913 Webster]

   2. To put a new sole or heel on; as, to tap shoes.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tapping
    n 1: the sound of light blow or knock; "he heard the tapping of
         the man's cane"

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "tapping":
   aspiration, banging, blasting, bleeding, bloodletting, broaching,
   bursting, cracking, crashing, cupping, drafting, drainage,
   draining, drawing, emptying, exploding, explosive, flapping,
   knocking, milking, phlebotomy, pipetting, popping, pumping,
   rapping, siphoning, slapping, slatting, sucking, suction,
   venesection