An assassin is someone who murders an important political or religious leader. Brutus is one of the most infamous assassins in history. He murdered Julius Caesar, who ruled Rome in the first century B.C.
The word assassin, pronounced "uh-SASS-in," describes a person who murders a prominent person, like a political or religious leader. Often, this person is hired to kill, though he or she might act on personal motivations. To correctly spell assassin, remember that it has two double s's.