thief vs stealer

thief and stealer both are nouns.

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

As nouns, thief and stealer are synonyms defined as:

thief and stealer: a criminal who takes property belonging to someone else with the intention of keeping it or selling it

thief (noun)	stealer (noun)
a criminal who takes property belonging to someone else with the intention of keeping it or selling it	a criminal who takes property belonging to someone else with the intention of keeping it or selling it