Synonyms for Hammerhead (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, knucklehead, loggerhead, lunkhead, numskull, fuckhead, muttonhead, shithead, dumbassWordNet sense 2 (medium-sized live-bearing shark with eyes at either end of a flattened hammer-shaped head; worldwide in warm waters; can be dangerous):
hammerhead sharkFrom the ODE community, based on WordNetadd/edit