place down vs plunk

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

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

As verbs, plunk is a hyponym of place down; that is, plunk is a word with a more specific, narrower meaning than place down:

Other hyponyms of place down include flump, plank, plonk, plop, plump, plump down, plunk down.

place down (noun)	plunk (noun)
	(baseball) hitting a baseball so that it drops suddenly
	a hollow twanging sound

place down (verb)	plunk (verb)
cause to sit or seat or be in a settled position or place	pull lightly but sharply with a plucking motion
	set (something or oneself) down with or as if with a noise
	drop steeply
	make or move along with a sound as of a horse's hooves striking the ground

place down (adverb)	plunk (adverb)
	with a short hollow thud