From Arabic 'ḥashāshīn' (hashish users), a slur against the Nizārī sect whose targeted killings became legendary during the Crusades.
A person who murders an important person for political or religious reasons; a hired killer.
From Medieval Latin 'assassinus,' from Arabic 'ḥashīshiyyīn' (حشيشيين) or 'ḥashāshīn' (حشاشين), meaning 'hashish users.' The name was applied by enemies to the Nizārī Ismāʿīlī sect led by Ḥasan-i Ṣabbāḥ from the mountain fortress of Alamūt in Persia (1090–1256). The Crusaders encountered the sect in the Levant and transmitted lurid, largely propagandistic tales of drug-fueled killers
Marco Polo's account of the 'Old Man of the Mountain' who supposedly drugged young men with hashish and placed them in a garden paradise to convince them they had glimpsed heaven — thus securing their fanatical loyalty — is almost certainly fiction, but it became one of the most widely believed legends of the medieval world and cemented 'assassin' in European vocabulary.