Synonyms for Loggerhead (same or very similar meaning)
WordNet sense 1 (these words are used to express a low opinion of someone's intelligence):
blockhead, bonehead, dunce, dunderhead, hammerhead, knucklehead, lunkhead, numskull, fuckhead, muttonhead, shithead, dumbassWordNet sense 2 (very large carnivorous sea turtle; wide-ranging in warm open seas):
Caretta caretta, loggerhead turtleFrom the ODE community, based on WordNetadd/edit