mongoose vs ichneumon

mongoose and ichneumon both are nouns.

Word	Noun	Adjective	Verb	Adverb
mongoose	Yes	No	No	No
ichneumon	Yes	No	No	No

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

mongoose: agile grizzled Old World viverrine; preys on snakes and rodents
ichneumon: northern African mongoose; in ancient times thought to devour crocodile eggs

Other hyponyms of mongoose include Herpestes nyula, Indian mongoose, Herpestes ichneumon.

mongoose (noun)	ichneumon (noun)
agile grizzled Old World viverrine; preys on snakes and rodents	northern African mongoose; in ancient times thought to devour crocodile eggs