cattle thief vs rustler

cattle thief and rustler both are nouns.

Word	Noun	Adjective	Verb	Adverb
cattle thief	Yes	No	No	No
rustler	Yes	No	No	No

As nouns, cattle thief and rustler are synonyms defined as:

cattle thief and rustler: someone who steals livestock (especially cattle)

cattle thief (noun)	rustler (noun)
someone who steals livestock (especially cattle)	someone who steals livestock (especially cattle)