assassin

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One who murders by surprise attack, especially one who carries out a plot to kill a prominent person.
2. n. A member of a secret order of Muslims who terrorized and killed Christian Crusaders and others.

Century Dictionary and Cyclopedia

1. n. One of the Assassins, a military and religious order in Syria, founded in Persia by Hassan ben Sabbah about the year 1090. A colony migrated from Persia to Syria, settled in various places, with their chief seat on the mountains of Lebanon, and became remarkable for their secret murders in blind obedience to the will of their chief. Their religion was a compound of Magianism, Judaism, Christianity, and Mohammedanism. One article of their creed was that the Holy Spirit resided in their chief and that his orders proceeded from God himself. The chief of the sect is best known by the denomination old man of the mountain (Arabic sheikh al-jebal, chief of the mountains). These barbarous chieftains and their followers spread terror among nations far and near for almost two centuries. In the time of the crusades they mustered to the number of 50,000, and presented a formidable obstacle to the arms of the Christians. They were eventually subdued by the sultan Bibars about 1272.
2. n. One who undertakes, for a reward previously agreed on, to put another person to death by surprise or secret assault; hence, one who kills, or attempts to kill, by treacherous violence; a murderer.
3. n. A breast-knot, or similar decoration worn in front.
4. To murder; assassinate.

Wiktionary

1. n. historical A member of a Muslim militant group responsible for murdering Christian leaders during the Crusades.
2. n. Someone who intentionally kills a person, especially a professional who kills a public or political figure.
3. n. Any ruthless killer.
4. v. nonstandard To assassinate.

GNU Webster's 1913

1. n. One who kills, or attempts to kill, by surprise or secret assault; one who treacherously murders any one unprepared for defense.
2. v. obsolete To assassinate.

WordNet 3.0

1. n. a member of a secret order of Muslims (founded in the 12th century) who terrorized and killed Christian Crusaders
2. n. a murderer (especially one who kills a prominent political figure) who kills by a surprise attack and often is hired to do the deed