Hmmm...
Main Entry: cult
Pronunciation: ˈkəlt
Function: noun
Usage: often attributive
Etymology: French & Latin; French culte, from Latin cultus care, adoration, from colere to cultivate ? more at wheel
Date: 1617
1 : formal religious veneration : worship
2 : a system of religious beliefs and ritual; also : its body of adherents
3 : a religion regarded as unorthodox or spurious; also : its body of adherents
4 : a system for the cure of disease based on dogma set forth by its promulgator <health cults>
5 a : great devotion to a person, idea, object, movement, or work (as a film or book); especially : such devotion regarded as a literary or intellectual fad b : the object of such devotion c : a usually small group of people characterized by such devotion.
Cult
Main Entry: re?li?gion
Pronunciation: ri-ˈli-jən
Function: noun
Etymology: Middle English religioun, from Anglo-French religiun, Latin religion-, religio supernatural constraint, sanction, religious practice, perhaps from religare to restrain, tie back ? more at rely
Date: 13th century
1 a : the state of a religious <a nun in her 20th year of religion> b (1) : the service and worship of God or the supernatural (2) : commitment or devotion to religious faith or observance
2 : a personal set or institutionalized system of religious attitudes, beliefs, and practices
3 archaic : scrupulous conformity : conscientiousness
4 : a cause, principle, or system of beliefs held to with ardor and faith
Religion
I don't know about you, but I don't see much difference in the definitions.
The pastor of my church says the definition of a cult is 'the church down the street' (not literally).