An assassin is someone who is hired or driven to secretly kill an important person, often for political or religious reasons.
The word comes from Medieval Latin *assassinus*, from Arabic *ḥashshāshīn*, a nickname for a secretive medieval group. They were rumored (probably unfairly) to use hashish before missions, and the name stuck in European languages.
The fact that 'assassin' comes from a real historical group shows how powerful stories can be: legends about them shaped an entire word. Today we use it without thinking about that group at all, but the history is still hidden inside the sound.
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