octopod vs cephalopod mollusk

octopod and cephalopod mollusk both are nouns.

Word	Noun	Adjective	Verb	Adverb
octopod	Yes	No	No	No
cephalopod mollusk	Yes	No	No	No

As nouns, cephalopod mollusk is a hypernym of octopod; that is, cephalopod mollusk is a word with a broader meaning than octopod:

octopod: a cephalopod with eight arms but lacking an internal shell
cephalopod mollusk: marine mollusk characterized by well-developed head and eyes and sucker-bearing tentacles

Other hypernyms of octopod include cephalopod.

octopod (noun)	cephalopod mollusk (noun)
a cephalopod with eight arms but lacking an internal shell	marine mollusk characterized by well-developed head and eyes and sucker-bearing tentacles