lobster vs decapod crustacean

lobster and decapod crustacean both are nouns.

Word	Noun	Adjective	Verb	Adverb
lobster	Yes	No	No	No
decapod crustacean	Yes	No	No	No

As nouns, decapod crustacean is a hypernym of lobster; that is, decapod crustacean is a word with a broader meaning than lobster:

lobster: any of several edible marine crustaceans of the families Homaridae and Nephropsidae and Palinuridae
decapod crustacean: crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax

Other hypernyms of lobster include decapod.

lobster (noun)	decapod crustacean (noun)
any of several edible marine crustaceans of the families Homaridae and Nephropsidae and Palinuridae	crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax
flesh of a lobster