stealer vs plagiariser

stealer and plagiariser both are nouns.

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

As nouns, plagiariser is a hyponym of stealer; that is, plagiariser 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
plagiariser: someone who uses another person's words or ideas as if they were his own

stealer (noun)	plagiariser (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