ETYMOLOGY

The Assassins were finally linked by the 19th century orientalists scholar Silvestre de Sacy to the Arabic hashish using their variant names assassin and assissini in the 19th century. Citing the example of one of the first written applications of the Arabic term hashish to the Ismailis by 13th century historian Abu Shama, de Sacy demonstrated its connection to the name given to the Ismailis throughout Western scholarship. The first known usage of the term hashishi has been traced back to 1122 CE when the Fatimid caliph al-Āmir employed it in derogatory reference to the Syrian Nizaris.^{[Daftary 3]} Used figuratively, the term hashishi connoted meanings such as outcasts or rabble. Without actually accusing the group of utilizing the hashish drug, the Caliph used the term in a pejorative manner. This label was quickly adopted by anti-Ismaili historians and applied to the Ismailis of Syria and Persia. The spread of the term was further facilitated through military encounters between the Nizaris and the Crusaders, whose chroniclers adopted the term and disseminated it across Europe.
During the medieval period, Western scholarship on the Ismailis contributed to the popular view of the community as a radical sect of assassins, believed to be trained for the precise murder of their adversaries. By the 14th century CE, European scholarship on the topic had not advanced much beyond the work and tales from the Crusaders. The origins of the word forgotten, across Europe the term Assassin had taken the meaning of "professional murderer".^{[Daftary 6]} In 1603 the first Western publication on the topic of the Assassins was authored by a court official for King Henry IV and was mainly based on the narratives of Marco Polo from his visits to the Near East. While he assembled the accounts of many Western travelers, the author failed to explain the etymology of the term Assassin.
According to Lebanese writer Amin Maalouf:

Many scholars have argued, and demonstrated convincingly, that the attribution of the epithet 'hashish eaters' or 'hashish takers' is a misnomer derived from enemies of the Isma'ilis and was never used by Muslim chroniclers or sources. It was therefore used in a pejorative sense of 'enemies' or 'disreputable people'. This sense of the term survived into modern times with the common Egyptian usage of the term Hashasheen in the 1930s to mean simply 'noisy or riotous'. It is unlikely that the austere Hassan-i Sabbah indulged personally in drug taking. ...there is no mention of that drug hashish in connection with the Persian Assassins – especially in the library of Alamut ("the secret archives").

Another modern scholar states that:

[...] their contemporaries in the Muslim world would call them hash-ishiyun, "hashish-smokers"; some orientalists thought that this was the origin of the word "assassin", which in many European languages was more terrifying yet. ...The truth is different. According to texts that have come down to us from Alamut, Hassan-i Sabbah liked to call his disciples Asasiyun, meaning people who are faithful to the Asās, meaning "foundation" of the faith. This is the word, misunderstood by foreign travelers, that seemed similar to "hashish".