larcenist vs thief

larcenist and thief both are nouns.

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

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

larcenist: a person who commits larceny
thief: a criminal who takes property belonging to someone else with the intention of keeping it or selling it

Other hypernyms of larcenist include stealer.

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