1. A set of beliefs concerning the cause, nature, and purpose of the universe; especially, when considered as the creation of a superhuman agency or agencies, usually involving devotional and ritual observances, and often containing a moral code governing the conduct of human affairs.
2. A specific fundamental set of beliefs and practices generally agreed upon by a number of people or sects; such as, the Christian religion; the Islamic religion; the Buddhist religion.
3. The body of people adhering to a particular set of beliefs and practices.
4. A strong belief in a supernatural power or powers that control human destiny.
5. Etymology: "state of life bound by monastic vows", also "conduct indicating a belief in a divine power"; from Anglo-French religiun (11th century); from Old French religion, "religious community"; from Latin religionem, religio, "respect for what is sacred, reverence for the gods"; in Late Latin, "monastic life" (5th century).

According to Cicero, it was derived from relegare, "to go through again, to read again"; from re-, "again" + legere, "to read" (as with "lecture").

Popular etymology among the later ancients (and many modern writers) connects it with religare, "to bind fast", via the notion of "place an obligation on", or "bond between humans and gods".