A shark with a distinctively flattened, hammer-shaped head, or a stupid or stubborn person.
Compound word from 'hammer' (Old Norse 'hamarr') and 'head' (Old English 'heafod'). The shark was named for its unusual head shape; the insult meaning came later.
The hammerhead shark's weird head shape is actually brilliant engineering—those sensors spread wide let it scan a much larger area for electric signals from prey hiding in the sand. What looks funny is actually a superpower!
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