bonnethead vs hammerhead shark

bonnethead and hammerhead shark both are nouns.

Word	Noun	Adjective	Verb	Adverb
bonnethead	Yes	No	No	No
hammerhead shark	Yes	No	No	No

As nouns, hammerhead shark is a hypernym of bonnethead; that is, hammerhead shark is a word with a broader meaning than bonnethead:

bonnethead: small harmless hammerhead having a spade-shaped head; abundant in bays and estuaries
hammerhead shark: medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous

Other hypernyms of bonnethead include hammerhead.

bonnethead (noun)	hammerhead shark (noun)
small harmless hammerhead having a spade-shaped head; abundant in bays and estuaries	medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous