inquiry agent vs private eye

inquiry agent and private eye both are nouns.

Word	Noun	Adjective	Verb	Adverb
inquiry agent	Yes	No	No	No
private eye	Yes	No	No	No

As nouns, private eye is a hypernym of inquiry agent; that is, private eye is a word with a broader meaning than inquiry agent:

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

Other hypernyms of inquiry agent include operative, PI, private detective, private investigator, shamus, sherlock.

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