stealer vs plagiarist

stealer and plagiarist both are nouns.

Word	Noun	Adjective	Verb	Adverb
stealer	Yes	No	No	No
plagiarist	Yes	No	No	No

As nouns, plagiarist is a hyponym of stealer; that is, plagiarist is a word with a more specific, narrower meaning than stealer:

stealer: a criminal who takes property belonging to someone else with the intention of keeping it or selling it
plagiarist: someone who uses another person's words or ideas as if they were his own

stealer (noun)	plagiarist (noun)
a criminal who takes property belonging to someone else with the intention of keeping it or selling it	someone who uses another person's words or ideas as if they were his own