The Collaborative International Dictionary of English v.0.48:

Flatter \Flat"ter\ (fl[a^]t"t[~e]r), v. t. [imp. & p. p.
   Flattered; p. pr. & vb. n. Flattering.] [OE. flateren,
   cf. OD. flatteren; akin to G. flattern to flutter, Icel.
   fla[eth]ra to fawn, flatter: cf. F. flatter. Cf. Flitter,
   Flutter, Flattery.]
   1. To treat with praise or blandishments; to gratify or
      attempt to gratify the self-love or vanity of, esp. by
      artful and interested commendation or attentions; to
      blandish; to cajole; to wheedle.
      [1913 Webster]

            When I tell him he hates flatterers,
            He says he does, being then most flattered. --Shak.
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            A man that flattereth his neighbor, spreadeth a net
            for his feet.                         --Prov. xxix.
                                                  5.
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            Others he flattered by asking their advice.
                                                  --Prescott.
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   2. To raise hopes in; to encourage or favorable, but
      sometimes unfounded or deceitful, representations.
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   3. To portray too favorably; to give a too favorable idea of;
      as, his portrait flatters him.
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The Collaborative International Dictionary of English v.0.48:

Flattering \Flat"ter*ing\, a.
   That flatters (in the various senses of the verb); as, a
   flattering speech.
   [1913 Webster]

         Lay not that flattering unction to your soul. --Shak.
   [1913 Webster]

         A flattering painter, who made it his care,
         To draw men as they ought be, not as they are.
                                                  --Goldsmith.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flattering
    adj 1: showing or representing to advantage; "a flattering
           color" [ant: uncomplimentary, unflattering]

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "flattering":
   abject, acclamatory, admiring, adulatory, appreciative,
   approbatory, backscratching, becoming, beggarly, bland,
   blandishing, blarneying, bootlicking, buttery, cajoling,
   commendatory, complimentary, courtierly, courtly, cowering,
   crawling, cringing, crouching, encomiastic, enhancing, eulogistic,
   fair-spoken, fawning, fine-spoken, footlicking, fulsome,
   gratifying, groveling, gushing, hangdog, honey-mouthed,
   honey-tongued, honeyed, ingratiating, insincere, insinuating, kind,
   laudatory, mealymouthed, obeisant, obsequious, oily, oily-tongued,
   on bended knee, panegyric, parasitic, prostrate, regardful,
   respectful, slimy, slobbery, smarmy, smooth, smooth-spoken,
   smooth-tongued, sniveling, soapy, soft-soaping, sponging, sugary,
   sycophantic, timeserving, toadeating, toadying, toadyish,
   truckling, unctuous, wheedling