Having sharp points sticking out, or easily irritated and unfriendly in manner.
From 'spike,' which comes from Old Norse 'spíkr' meaning a nail or pointed object. The '-y' suffix was added to create an adjective. The word's physical meaning came first, then expanded metaphorically to describe people's sharp or prickly temperaments.
Plants developed spikes millions of years ago as armor against predators, and we borrowed the word 'spiky' to describe both physical and emotional defensiveness. When we say someone is 'spiky,' we're comparing their personality to a porcupine's quills—a natural and ancient defense mechanism. It's a great example of how animals teach us vocabulary through their survival strategies.
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