The Collaborative International Dictionary of English v.0.48:

Devotion \De*vo"tion\, n. [F. d['e]votion, L. devotio.]
   1. The act of devoting; consecration.
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   2. The state of being devoted; addiction; eager inclination;
      strong attachment love or affection; zeal; especially,
      feelings toward God appropriately expressed by acts of
      worship; devoutness.
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            Genius animated by a fervent spirit of devotion.
                                                  --Macaulay.
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   3. Act of devotedness or devoutness; manifestation of strong
      attachment; act of worship; prayer. "The love of public
      devotion." --Hooker.
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   4. Disposal; power of disposal. [Obs.]
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            They are entirely at our devotion, and may be turned
            backward and forward, as we please.   --Godwin.
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   5. A thing consecrated; an object of devotion. [R.]
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            Churches and altars, priests and all devotions,
            Tumbled together into rude chaos.     --Beau. & Fl.
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   Days of devotion. See under Day.

   Syn: Consecration; devoutness; religiousness; piety;
        attachment; devotedness; ardor; earnestness.
        [1913 Webster]

WordNet (r) 3.0 (2006):

devotion
    n 1: feelings of ardent love; "their devotion to each other was
         beautiful" [syn: devotion, devotedness]
    2: commitment to some purpose; "the devotion of his time and
       wealth to science"
    3: religious zeal; the willingness to serve God [syn:
       idolatry, devotion, veneration, cultism]
    4: (usually plural) religious observance or prayers (usually
       spoken silently); "he returned to his devotions"

Moby Thesaurus II by Grady Ward, 1.0:

224 Moby Thesaurus words for "devotion":
   Amor, Christian love, Eros, Platonic love, abandon, adherence,
   adhesion, admiration, adoration, affection, agape, allegiance,
   altruism, ardency, ardor, assigned task, attachment, beatification,
   beatitude, blessedness, blessing, bodily love, bona fides, bond,
   bonne foi, bounden duty, brotherly love, burden, business,
   call of duty, canonization, caritas, charge, charity, churchgoing,
   co-worship, commitment, committedness, conformity, conjugal love,
   consecration, constancy, cult, cultism, cultus, decidedness,
   decision, decisiveness, dedication, deference, definiteness,
   desire, determinateness, determination, determinedness, devoir,
   devotedness, devoutness, disinterest, disinterestedness, dulia,
   duties and responsibilities, dutifulness, duty, eagerness,
   earnestness, enshrinement, enthusiasm, ethics, exaltation, faith,
   faithful love, faithfulness, fanaticism, fancy, fastness, fealty,
   fervency, fervidness, fervor, fidelity, fire, firmness, flame,
   fondness, free love, free-lovism, glorification, godliness,
   good faith, grace, hallowing, heart, heartiness, heat, heatedness,
   hero worship, holiness, homage, humility, hyperdulia, idolatry,
   idolism, idolization, impassionedness, imperative, infatuation,
   intensity, intentness, justification, justification by works,
   lasciviousness, latria, libido, like, liking, line of duty, love,
   love of God, lovemaking, loyalty, married love, mission, modesty,
   must, obligation, observance, obstinacy, onus, ordainment,
   ordination, ought, passion, passionateness, perseverance,
   persistence, physical love, pietism, piety, piousness, place,
   popular regard, popularity, prayer, prostration, purification,
   purpose, purposefulness, readiness, regard, relentlessness,
   religion, religionism, religiosity, religiousness, resoluteness,
   resolution, resolve, resolvedness, respect, reverence, ritual,
   sacrifice, sainthood, sainting, sanctification, sanctity,
   self-abasement, self-abnegation, self-denial, self-devotion,
   self-effacement, self-forgetfulness, self-immolation,
   self-imposed duty, self-neglect, self-neglectfulness,
   self-renouncement, self-sacrifice, self-subjection, self-will,
   selflessness, sentiment, seriousness, setting apart, sex,
   sexual love, shine, sincerity, single-mindedness, spirit,
   spiritual love, spirituality, state of grace, staunchness,
   steadfastness, tenacity, tender feeling, tender passion, theism,
   tie, total commitment, transcendent wonder, tried-and-trueness,
   triedness, troth, true blue, truelove, trueness, unacquisitiveness,
   unpossessiveness, unselfishness, uxoriousness, vehemence,
   veneration, warmth, weakness, will, willingness, worship,
   worshipfulness, worshiping, yearning, zeal