plunderer vs thief

plunderer and thief both are nouns.

Word	Noun	Adjective	Verb	Adverb
plunderer	Yes	No	No	No
thief	Yes	No	No	No

As nouns, thief is a hypernym of plunderer; that is, thief is a word with a broader meaning than plunderer:

plunderer: someone who takes spoils or plunder (as in war)
thief: a criminal who takes property belonging to someone else with the intention of keeping it or selling it

Other hypernyms of plunderer include stealer.

plunderer (noun)	thief (noun)
someone who takes spoils or plunder (as in war)	a criminal who takes property belonging to someone else with the intention of keeping it or selling it