loggerhead vs sea turtle

loggerhead and sea turtle both are nouns.

Word	Noun	Adjective	Verb	Adverb
loggerhead	Yes	No	No	No
sea turtle	Yes	No	No	No

As nouns, sea turtle is a hypernym of loggerhead; that is, sea turtle is a word with a broader meaning than loggerhead:

loggerhead: very large carnivorous sea turtle; wide-ranging in warm open seas
sea turtle: any of various large turtles with limbs modified into flippers; widely distributed in warm seas

Other hypernyms of loggerhead include marine turtle.

loggerhead (noun)	sea turtle (noun)
very large carnivorous sea turtle; wide-ranging in warm open seas	any of various large turtles with limbs modified into flippers; widely distributed in warm seas
a stupid person; these words are used to express a low opinion of someone's intelligence