octopod vs nautilus

octopod and nautilus both are nouns.

Word	Noun	Adjective	Verb	Adverb
octopod	Yes	No	No	No
nautilus	Yes	No	No	No

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

octopod: a cephalopod with eight arms but lacking an internal shell
nautilus: cephalopod mollusk of warm seas whose females have delicate papery spiral shells

Other hyponyms of octopod include devilfish, octopus, Argonaut, Argonauta argo, paper nautilus.

octopod (noun)	nautilus (noun)
a cephalopod with eight arms but lacking an internal shell	cephalopod of the Indian and Pacific oceans having a spiral shell with pale pearly partitions
	cephalopod mollusk of warm seas whose females have delicate papery spiral shells
	a submarine that is propelled by nuclear power