Caliphate became the top lookup on Merriam-Webster.com on February 8, 2011.
Glenn Beck used the word to describe what he believes will be the outcome of political unrest in the Middle East.
By caliphate, he means rule of the entire Islamic world by a single civic and spiritual leader, called a caliph.
The original caliphates grew through expansion and conquest in the centuries following the death of the Prophet Muhammad in A.D. 632. Caliphate has become a hot-button term associated with al-Qaeda's goal of restoring the Islamic caliphate.
The word comes from the Arabic word meaning "successor," since a caliph was viewed as a successor to Mohammed.
Photo credit: Nir Nussbaum / flickr