plunk vs plunk down

plunk is a noun but plunk down is not a noun.

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

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

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

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

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

plunk (verb)	plunk down (verb)
pull lightly but sharply with a plucking motion	set (something or oneself) down with or as if with a noise
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

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