shamus vs inquiry agent

shamus and inquiry agent both are nouns.

Word	Noun	Adjective	Verb	Adverb
shamus	Yes	No	No	No
inquiry agent	Yes	No	No	No

As nouns, inquiry agent is a hyponym of shamus; that is, inquiry agent is a word with a more specific, narrower meaning than shamus:

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

Other hyponyms of shamus include hotel detective, house detective, house dick, store detective.

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