place down vs plank

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

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

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

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

place down (noun)	plank (noun)
	an endorsed policy in the platform of a political party
	a stout length of sawn timber; made in a wide variety of sizes and used for many purposes

place down (verb)	plank (verb)
cause to sit or seat or be in a settled position or place	cook and serve on a plank
	cover with planks
	set (something or oneself) down with or as if with a noise