The Collaborative International Dictionary of English v.0.48:

Respectable \Re*spect"a*ble\ (-?-b'l), a. [F. respectable, LL.
   respectabilis.]
   1. Worthy of respect; fitted to awaken esteem; deserving
      regard; hence, of good repute; not mean; as, a respectable
      citizen. "The respectable quarter of Sicca." --J. H.
      Newman.
      [1913 Webster]

            No government, any more than an individual, will
            long be respected, without being truly respectable.
                                                  --Madison.
      [1913 Webster]

   2. Moderate in degree of excellence or in number; as, a
      respectable performance; a respectable audience.
      [1913 Webster] --Re*spect"a*ble*ness,n. --
      Re*spect"a*bly, adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

respectable
    adj 1: characterized by socially or conventionally acceptable
           morals; "a respectable woman" [ant: unrespectable]
    2: deserving of esteem and respect; "all respectable companies
       give guarantees"; "ruined the family's good name" [syn:
       estimable, good, honorable, respectable]
    3: large in amount or extent or degree; "it cost a considerable
       amount"; "a goodly amount"; "received a hefty bonus"; "a
       respectable sum"; "a tidy sum of money"; "a sizable fortune"
       [syn: goodly, goodish, healthy, hefty, respectable,
       sizable, sizeable, tidy]

Moby Thesaurus II by Grady Ward, 1.0:

147 Moby Thesaurus words for "respectable":
   Christian, OK, acceptable, adequate, admissible, all right,
   appreciable, appropriate, becoming, befitting, better than nothing,
   betwixt and between, blameless, chaste, clean, comely, conforming,
   considerable, correct, creditable, decent, decorous, demure,
   dignified, done, dull, erect, esteemed, estimable, ethical, fair,
   fair to middling, fairish, fate, full of integrity, genteel, good,
   good enough, goodish, goodly, held in esteem, high-minded,
   high-principled, highly esteemed, highly regarded, highly reputed,
   highly respectable, honest, honorable, honored, immaculate,
   in favor, in good odor, in high favor, indifferent, innocent,
   insipid, inviolate, irreproachable, just, lackluster, law-abiding,
   law-loving, law-revering, manly, mediocre, medium, meritorious,
   middling, moderate, modest, moral, namby-pamby, nice, noble,
   not amiss, not bad, not half bad, not so bad, of a kind, of a sort,
   of sorts, okay, passable, presentable, prestigious, pretty good,
   principled, proper, pure, reasonable, refined, reputable, reputed,
   respected, revered, reverend, right, right-minded, righteous,
   satisfactory, seemly, sensible, significant, sizable, sizeable,
   smart, so-so, spotless, stainless, sterling, substantial,
   sufficient, suitable, tedious, tidy, tolerable, true-dealing,
   true-devoted, true-disposing, true-souled, true-spirited,
   truehearted, unblemished, uncorrupt, uncorrupted, undefiled,
   unexceptionable, unimpeachable, unobjectionable, unspotted,
   unstained, unsullied, untarnished, upright, uprighteous,
   upstanding, vapid, venerable, venerated, virtuous, well-thought-of,
   wishy-washy, workmanlike, worshipful, worthy, yeomanly