investigator vs gumshoe

investigator and gumshoe both are nouns.

Word	Noun	Adjective	Verb	Adverb
investigator	Yes	No	No	No
gumshoe	Yes	No	No	No

As nouns, gumshoe is a hyponym of investigator; that is, gumshoe is a word with a more specific, narrower meaning than investigator:

Other hyponyms of investigator include dick, hawkshaw, plainclothesman, tracer.

investigator (noun)	gumshoe (noun)
someone who investigates	a waterproof overshoe that protects shoes from water or snow
a scientist who devotes himself to doing research	someone who is a detective
a police officer who investigates crimes