hoarder vs pack rat

hoarder and pack rat both are nouns.

Word	Noun	Adjective	Verb	Adverb
hoarder	Yes	No	No	No
pack rat	Yes	No	No	No

As nouns, pack rat is a hyponym of hoarder; that is, pack rat is a word with a more specific, narrower meaning than hoarder:

Other hyponyms of hoarder include magpie, scavenger, miser, churl, niggard, scrooge, skinflint, penny pincher.

hoarder (noun)	pack rat (noun)
a person who accumulates things and hides them away for future use	any of several bushy-tailed rodents of the genus Neotoma of western North America; hoards food and other objects
	someone who collects things that have been discarded by others