private eye vs private detective

private eye and private detective both are nouns.

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

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

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

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

private eye (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