Source : Webster's Revised Unabridged Dictionary (1913)

Plunk \Plunk\, v. t. [Imitative.] [Chiefly Colloq.]
   1. To pluck and release quickly (a musical string); to twang.

   2. To throw, push, drive heavily, plumply, or suddenly; as,
      to plunk down a dollar; also, to hit or strike.

   3. To be a truant from (school). [Scot.]

Plunk \Plunk\, v. i. [Chiefly Colloq.]
   1. To make a quick, hollow, metallic, or harsh sound, as by
      pulling hard on a taut string and quickly releasing it; of
      a raven, to croak.

   2. To drop or sink down suddenly or heavily; to plump.

   3. To play truant, or ``hooky''. [Scot.]

Plunk \Plunk\, n.
   1. Act or sound of plunking. [Colloq.]

   2. [Slang]
      (a) A large sum of money. [Obs.]
      (b) A dollar. [U. S.]

Source : WordNet®

plunk
     n 1: a hollow twanging sound
     2: (baseball) hitting a baseball so that it drops suddenly
        [syn: {plunker}]
     adv : with a short hollow thud; "plop came the ball down to the
           corner of the green" [syn: {plop}]
     v 1: make or move along with a sound as of a horse's hooves
          striking the ground [syn: {clop}, {clump}, {clunk}]
     2: set (something or oneself) down with or as if with a noise;
        "He planked the money on the table"; "He planked himself
        into the sofa" [syn: {plank}, {flump}, {plonk}, {plop}, {plump
        down}, {plunk down}, {plump}]
     3: drop steeply; "the stock market plunged" [syn: {dive}, {plunge}]
     4: pull lightly but sharply with a plucking motion; "he plucked
        the strings of his mandolin" [syn: {pluck}, {pick}]