explorer vs frogman

explorer and frogman both are nouns.

Word	Noun	Adjective	Verb	Adverb
explorer	Yes	No	No	No
frogman	Yes	No	No	No

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

explorer: someone who travels into little known regions (especially for some scientific purpose)
frogman: someone who works underwater

explorer (noun)	frogman (noun)
someone who travels into little known regions (especially for some scientific purpose)	someone who works underwater