private investigator vs private detective

private investigator and private detective both are nouns.

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

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

private investigator and private detective: 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 eye, shamus, sherlock.

private investigator (noun)	private detective (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