The Collaborative International Dictionary of English v.0.48:

Soothe \Soothe\ (s[=oo][th]), v. t. [imp. & p. p. Soothed; p.
   pr. & vb. n. Soothing.] [Originally, to assent to as true;
   OE. so[eth]ien to verify, AS. ges[=o][eth]ian to prove the
   truth of, to bear witness. See Sooth, a.]
   1. To assent to as true. [Obs.] --Testament of Love.
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   2. To assent to; to comply with; to gratify; to humor by
      compliance; to please with blandishments or soft words; to
      flatter.
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            Good, my lord, soothe him, let him take the fellow.
                                                  --Shak.
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            I've tried the force of every reason on him,
            Soothed and caressed, been angry, soothed again.
                                                  --Addison.
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   3. To assuage; to mollify; to calm; to comfort; as, to soothe
      a crying child; to soothe one's sorrows.
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            Music hath charms to soothe the savage breast,
            To soften rocks, or bend a knotted oak. --Congreve.
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            Though the sound of Fame
            May for a moment soothe, it can not slake
            The fever of vain longing.            --Byron.
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   Syn: To soften; assuage; allay; compose; mollify;
        tranquilize; pacify; mitigate.
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The Collaborative International Dictionary of English v.0.48:

Soothing \Sooth"ing\,
   a. & n. from Soothe, v.
   [1913 Webster]

WordNet (r) 3.0 (2006):

soothing
    adj 1: affording physical relief; "a soothing ointment for her
           sunburn"
    2: freeing from fear and anxiety [syn: assuasive, soothing]

Moby Thesaurus II by Grady Ward, 1.0:

125 Moby Thesaurus words for "soothing":
   United Nations troops, abatement, allayment, alleviating,
   alleviation, alleviative, analgesia, analgesic, anesthesia,
   anesthetic, anesthetizing, anodyne, appeasement, appeasing,
   assuagement, assuasive, balmy, balsamic, benumbing, blunting, calm,
   calmant, calmative, calming, cathartic, cleansing, comforting,
   conciliation, conciliatory, cradling, damping, deadening,
   demulcent, demulsion, depressant, detente, diminishment,
   diminution, dreamy, drowsy, dulcification, dulling, ease, easement,
   easing, easing of relations, emollient, falling-off, gentling,
   hushing, hypnotic, irenic, leniency, lenitive, lessening, letdown,
   letup, lightening, loosening, lubricant, lubricating,
   lubricational, lubricative, lulling, mediation, mitigating,
   mitigation, mitigative, modulation, mollification, mollifying,
   narcotic, numbing, pacific, pacification, pacificatory, pacifying,
   pain-killing, palliation, palliative, paregoric,
   peace-keeping force, peaceful, peacemaking, peacemongering,
   placability, placation, placative, placatory, propitiation,
   propitiative, propitiatory, purgative, quiet, quietening, quieting,
   reconciliatory, reduction, relaxation, relaxation of tension,
   relaxing, relief, relieving, remedial, remedy, remission, restful,
   rocking, salving, sedative, serene, slackening, sleep-inducing,
   soft, softening, somnifacient, somniferous, soothful, soporific,
   stilling, subduement, subduing, tempering, tranquilization,
   tranquilizing