plunk down vs plonk

plunk down is not a noun while plonk is a noun.

Word	Noun	Adjective	Verb	Adverb
plunk down	No	No	Yes	No
plonk	Yes	No	Yes	No

As verbs, plunk down and plonk are synonyms defined as:

plunk down and plonk: set (something or oneself) down with or as if with a noise

Other synonyms of plunk down include flump, plank, plop, plump, plump down, plunk.

plunk down (noun)	plonk (noun)
	the noise of something dropping (as into liquid)
	a cheap wine of inferior quality

plunk down (verb)	plonk (verb)
set (something or oneself) down with or as if with a noise	set (something or oneself) down with or as if with a noise