cult

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A religion or religious sect generally considered to be extremist or false, with its followers often living in an unconventional manner under the guidance of an authoritarian, charismatic leader.
• noun The followers of such a religion or sect.
• noun A system or community of religious worship and ritual.
• noun The formal means of expressing religious reverence; religious ceremony and ritual.
• noun A usually nonscientific method or regimen claimed by its originator to have exclusive or exceptional power in curing a particular disease.
• noun Obsessive, especially faddish, devotion to or veneration for a person, principle, or thing.
• noun The object of such devotion.
• noun An exclusive group of persons sharing an esoteric, usually artistic or intellectual interest.

from The Century Dictionary.

• noun Homage; worship; by extension, devoted attention to or veneration for a particular person or thing: as, the Shaksperian cult.
• noun A system of religious belief and worship; especially, the rites and ceremonies employed in worship. Also cultus.
• noun A subject of devoted attention or study; that in which one is earnestly or absorbingly interested.

from the GNU version of the Collaborative International Dictionary of English.

• noun Attentive care; homage; worship.
• noun A system of religious belief and worship.
• noun A system of intense religious veneration of a particular person, idea, or object, especially one considered spurious or irrational by traditional religious bodies.
• noun The group of individuals who adhere to a cult (senses 2 or 3).
• noun A strong devotion or interest in a particular person, idea or thing without religious associations, or the people holding such an interest.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A group of people with a religious, philosophical or cultural identity sometimes viewed as a sect, often existing on the margins of society or exploitative towards its members.
• noun Devotion to a saint.
• adjective Of, or relating to a cult.
• adjective Enjoyed by a small, loyal group.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun followers of an exclusive system of religious beliefs and practices
• noun followers of an unorthodox, extremist, or false religion or sect who often live outside of conventional society under the direction of a charismatic leader
• noun a system of religious beliefs and rituals
• noun a religion or sect that is generally considered to be unorthodox, extremist, or false
• noun an interest followed with exaggerated zeal