private investigator vs shamus

private investigator and shamus both are nouns.

Word	Noun	Adjective	Verb	Adverb
private investigator	Yes	No	No	No
shamus	Yes	No	No	No

As nouns, private investigator and shamus are synonyms defined as:

private investigator and shamus: someone who can be employed as a detective to collect information and assist in criminal investigations

Other synonyms of private investigator include operative, PI, private detective, private eye, sherlock.

private investigator (noun)	shamus (noun)
someone who can be employed as a detective to collect information and assist in criminal investigations	someone who can be employed as a detective to collect information and assist in criminal investigations