The Collaborative International Dictionary of English v.0.48:

Religion \Re*li"gion\ (r[-e]*l[i^]j"[u^]n), n. [F., from L.
   religio; cf. religens pious, revering the gods, Gr. 'ale`gein
   to heed, have a care. Cf. Neglect.]
   1. The outward act or form by which men indicate their
      recognition of the existence of a god or of gods having
      power over their destiny, to whom obedience, service, and
      honor are due; the feeling or expression of human love,
      fear, or awe of some superhuman and overruling power,
      whether by profession of belief, by observance of rites
      and ceremonies, or by the conduct of life; a system of
      faith and worship; a manifestation of piety; as, ethical
      religions; monotheistic religions; natural religion;
      revealed religion; the religion of the Jews; the religion
      of idol worshipers.
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            An orderly life so far as others are able to observe
            us is now and then produced by prudential motives or
            by dint of habit; but without seriousness there can
            be no religious principle at the bottom, no course
            of conduct from religious motives; in a word, there
            can be no religion.                   --Paley.
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            Religion [was] not, as too often now, used as
            equivalent for godliness; but . . . it expressed the
            outer form and embodiment which the inward spirit of
            a true or a false devotion assumed.   --Trench.
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            Religions, by which are meant the modes of divine
            worship proper to different tribes, nations, or
            communities, and based on the belief held in common
            by the members of them severally. . . . There is no
            living religion without something like a doctrine.
            On the other hand, a doctrine, however elaborate,
            does not constitute a religion.       --C. P. Tiele
                                                  (Encyc.
                                                  Brit.).
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            Religion . . . means the conscious relation between
            man and God, and the expression of that relation in
            human conduct.                        --J.
                                                  K["o]stlin
                                                  (Schaff-Herzog
                                                  Encyc.)
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            After the most straitest sect of our religion I
            lived a Pharisee.                     --Acts xxvi.
                                                  5.
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            The image of a brute, adorned
            With gay religions full of pomp and gold. --Milton.
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   2. Specifically, conformity in faith and life to the precepts
      inculcated in the Bible, respecting the conduct of life
      and duty toward God and man; the Christian faith and
      practice.

   Note: This definition is from the 1913 Webster, which was
         edited by Noah Porter, a theologian. His bias toward
         the Christion religion is evident not only in this
         definition, but in others as well as in the choice of
         quations or illustrative phrases. Caveat lector. - PJC
         [1913 Webster]

               Let us with caution indulge the supposition that
               morality can be maintained without religion.
                                                  --Washington.
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               Religion will attend you . . . as a pleasant and
               useful companion in every proper place, and every
               temperate occupation of life.      --Buckminster.
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   3. (R. C. Ch.) A monastic or religious order subject to a
      regulated mode of life; the religious state; as, to enter
      religion. --Trench.
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            A good man was there of religion.     --Chaucer.
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   4. Strictness of fidelity in conforming to any practice, as
      if it were an enjoined rule of conduct. [R.]
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            Those parts of pleading which in ancient times might
            perhaps be material, but at this time are become
            only mere styles and forms, are still continued with
            much religion.                        --Sir M. Hale.
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   Note: Religion, as distinguished from theology, is
         subjective, designating the feelings and acts of men
         which relate to God; while theology is objective, and
         denotes those ideas which man entertains respecting the
         God whom he worships, especially his systematized views
         of God. As distinguished from morality, religion
         denotes the influences and motives to human duty which
         are found in the character and will of God, while
         morality describes the duties to man, to which true
         religion always influences. As distinguished from
         piety, religion is a high sense of moral obligation and
         spirit of reverence or worship which affect the heart
         of man with respect to the Deity, while piety, which
         first expressed the feelings of a child toward a
         parent, is used for that filial sentiment of veneration
         and love which we owe to the Father of all. As
         distinguished from sanctity, religion is the means by
         which sanctity is achieved, sanctity denoting primarily
         that purity of heart and life which results from
         habitual communion with God, and a sense of his
         continual presence.
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   Natural religion, a religion based upon the evidences of a
      God and his qualities, which is supplied by natural
      phenomena. See Natural theology, under Natural.

   Religion of humanity, a name sometimes given to a religion
      founded upon positivism as a philosophical basis.

   Revealed religion, that which is based upon direct
      communication of God's will to mankind; especially, the
      Christian religion, based on the revelations recorded in
      the Old and New Testaments.
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WordNet (r) 3.0 (2006):

revealed religion
    n 1: a religion founded primarily on the revelations of God to
         humankind