put down vs plunk down

put down and plunk down both are verbs.

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

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

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

put down (verb)	plunk down (verb)
put down in writing; of texts, musical compositions, etc.	set (something or oneself) down with or as if with a noise
make a record of; set down in permanent form
put in a horizontal position
remove (cargo, people, etc.) from and leave
cause to sit or seat or be in a settled position or place
put (an animal) to death
reduce in worth or character, usually verbally
cause to come to the ground