Definition of "Alamut"

A castle in Iran and the most famous stronghold of the Nizari Ismailis, also known as the Assassins.  examples

A region in the modern-day Qazvin province of Iran in which the castle is located; Rudbar-i Alamut (Rudbar of Alamut)  examples

A period in the history of the Nizari Ismailism beginning from the capture of the castle in 1090 AD until its capitulation to the Mongols in 1256 AD.  examples