The Collaborative International Dictionary of English v.0.48:

Religious \Re*li"gious\, n.
   A person bound by monastic vows, or sequestered from secular
   concern, and devoted to a life of piety and religion; a monk
   or friar; a nun. --Addison.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Religious \Re*li"gious\ (r?-l?j"?s), a. [OF. religius,
   religious, F. religieux, from L. religiosus. See Religion.]
   1. Of or pertaining to religion; concerned with religion;
      teaching, or setting forth, religion; set apart to
      religion; as, a religious society; a religious sect; a
      religious place; religious subjects, books, teachers,
      houses, wars.
      [1913 Webster]

            Our law forbids at their religious rites
            My presence.                          --Milton.
      [1913 Webster]

   2. Possessing, or conforming to, religion; pious; godly; as,
      a religious man, life, behavior, etc.
      [1913 Webster]

            Men whose lives
            Religious titled them the sons of God. --Mlton
      [1913 Webster]

   3. Scrupulously faithful or exact; strict.
      [1913 Webster]

            Thus, Indianlike,
            Religious in my error, I adore
            The sun, that looks upon his worshiper. --Shak.
      [1913 Webster]

   4. Belonging to a religious order; bound by vows.
      [1913 Webster]

            One of them is religious.             --Chaucer.
      [1913 Webster]

   Syn: Pious; godly; holy; devout; devotional; conscientious;
        strict; rogod; exact.
        [1913 Webster]

WordNet (r) 3.0 (2006):

religious
    adj 1: concerned with sacred matters or religion or the church;
           "religious texts"; "a member of a religious order";
           "lords temporal and spiritual"; "spiritual leaders";
           "spiritual songs" [syn: religious, spiritual]
    2: having or showing belief in and reverence for a deity; "a
       religious man"; "religious attitude" [ant: irreligious]
    3: of or relating to clergy bound by monastic vows; "the
       religious or regular clergy conducts the service" [ant:
       secular]
    4: extremely scrupulous and conscientious; "religious in
       observing the rules of health"
    n 1: a member of a religious order who is bound by vows of
         poverty and chastity and obedience

Moby Thesaurus II by Grady Ward, 1.0:

157 Moby Thesaurus words for "religious":
   Christian, Christianlike, Christianly, God-fearing, Mariological,
   abbacomes, abbot, accurate, adoring, anthropomorphic,
   anthropotheistic, ascetic, attentive, awesome, awful, beadsman,
   believing, brother, caloyer, canonic, careful, celibate, cenobite,
   churchgoing, close, conscientious, constant, conventual,
   conventual prior, correct, cosmotheistic, critical, cultish,
   cultist, cultistic, deistic, delicate, demanding, detailed,
   devoted, devout, direct, ditheistic, divine, doctrinal, doctrinary,
   dutiful, ethical, even, exact, exacting, exigent, express,
   exquisite, faithful, fastidious, fine, finical, finicking, finicky,
   friar, fussy, godly, grand prior, heavenly, hermit, hieromonach,
   holy, honest, honorable, ineffable, inenarrable, inerrable,
   inerrant, inexpressible, infallible, inviolable, inviolate, just,
   lay abbot, lay brother, mathematical, mendicant, meticulous,
   micrometrically precise, microscopic, minute, monastic, monk,
   monotheistic, moral, narrow, nice, noble, numinous,
   overconscientious, overscrupulous, palmer, pantheistic, particular,
   physicomorphic, physicotheological, pietistic, pilgrim,
   pillar saint, pillarist, pinpoint, pious, polytheistic, prayerful,
   precise, precisianistic, precisionistic, prior, punctilious,
   punctual, refined, religieux, religiously exact, reverent,
   reverential, righteous, rigid, rigorous, sacred, sacrosanct,
   scientific, scientifically exact, scrupulous, scrutinizing, severe,
   solemn, spiritual, spiritual-minded, square, staunch, steadfast,
   strict, stylite, subtle, tender-conscienced, theistic, theological,
   tritheistic, true, undeviating, unerring, unspeakable, unswerving,
   untouchable, unutterable, upright, venerable, venerational,
   venerative, virtuous, worshipful