any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter
a murderer (especially one who kills a prominent political figure) who kills by a treacherous surprise attack and often is hired to do the deed; "his assassins were hunted down like animals"; "assassinators of kings and emperors"
a member of a secret order of Muslims (founded in the 12th century) who terrorized and killed Christian Crusaders