Nouns

(n)plunka hollow twanging sound
(n)plunk, plunker(baseball) hitting a baseball so that it drops suddenly

Verbs

(v)clop, clump, clunk, plunkmake or move along with a sound as of a horse's hooves striking the ground
(v)plank, flump, plonk, plop, plunk, plump down, plunk down, plumpset (something or oneself) down with or as if with a noise“He planked the money on the table”, “He planked himself into the sofa”
(v)dive, plunge, plunkdrop steeply“the stock market plunged”
(v)pluck, plunk, pickpull lightly but sharply with a plucking motion“he plucked the strings of his mandolin”

Adverbs

(r)plop, plunkwith a short hollow thud“plop came the ball down to the corner of the green”