The Collaborative International Dictionary of English v.0.48:

Assuage \As*suage"\, v. t. [imp. & p. p. Assuaged; p. pr. &
   vb. n. Assuaging.] [OE. asuagen, aswagen, OF. asoagier,
   asuagier, fr. assouagier, fr. L. ad + suavis sweet. See
   Sweet.]
   To soften, in a figurative sense; to allay, mitigate, ease,
   or lessen, as heat, pain, or grief; to appease or pacify, as
   passion or tumult; to satisfy, as appetite or desire.
   [1913 Webster]

         Refreshing winds the summer's heat assuage. --Addison.
   [1913 Webster]

         To assuage the sorrows of a desolate old man --Burke.
   [1913 Webster]

         The fount at which the panting mind assuages
         Her thirst of knowledge.                 --Byron.
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   Syn: To alleviate; mitigate; appease; soothe; calm;
        tranquilize; relieve. See Alleviate.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Assuage \As*suage"\, v. i.
   To abate or subside. [Archaic] "The waters assuaged." --Gen.
   vii. 1.
   [1913 Webster]

         The plague being come to a crisis, its fury began to
         assuage.                                 --De Foe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

assuage
    v 1: cause to be more favorably inclined; gain the good will of;
         "She managed to mollify the angry customer" [syn: pacify,
         lenify, conciliate, assuage, appease, mollify,
         placate, gentle, gruntle]
    2: satisfy (thirst); "The cold water quenched his thirst" [syn:
       quench, slake, allay, assuage]
    3: provide physical relief, as from pain; "This pill will
       relieve your headaches" [syn: relieve, alleviate,
       palliate, assuage]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "assuage":
   abate, adjust to, allay, alleviate, alter, anesthetize, appease,
   attemper, bank the fire, benumb, blunt, box in, chasten,
   circumscribe, condition, constrain, control, cushion, damp, dampen,
   de-emphasize, deaden, deaden the pain, diminish, downplay, dull,
   ease, ease matters, extenuate, feast, feed, foment, give relief,
   gratify, hedge, hedge about, keep within bounds, lay, leaven,
   lenify, lessen, lighten, limit, lull, mitigate, moderate, modify,
   modulate, mollify, narrow, numb, obtund, pad, palliate, play down,
   poultice, pour balm into, pour oil on, qualify, quench, reduce,
   reduce the temperature, regale, regulate by, relieve, restrain,
   restrict, salve, sate, satiate, satisfy, season, set conditions,
   set limits, slacken, slake, slow down, smother, sober, sober down,
   soften, soothe, stifle, stupe, subdue, suppress, tame, temper,
   tone down, tune down, underplay, weaken