The Collaborative International Dictionary of English v.0.48:

Ignoble \Ig*no"ble\, a. [L. ignobilis; pref. in- not + nobilis
   noble: cf. F. ignoble. See In- not, and Noble, a.]
   1. Of low birth or family; not noble; not illustrious;
      plebeian; common; humble.
      [1913 Webster]

            I was not ignoble of descent.         --Shak.
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            Her royal stock graft with ignoble plants. --Shak.
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   2. Not honorable, elevated, or generous; base.
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            'T is but a base, ignoble mind,
            That mounts no higher than a bird can soar. --Shak.
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            Far from the madding crowd's ignoble strife. --Gray.
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   3. (Zool.) Not a true or noble falcon; -- said of certain
      hawks, as the goshawk.

   Syn: Degenerate; degraded; mean; base; dishonorable;
        reproachful; disgraceful; shameful; scandalous;
        infamous.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Ignoble \Ig*no"ble\, v. t.
   To make ignoble. [Obs.] --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ignoble
    adj 1: completely lacking nobility in character or quality or
           purpose; "something cowardly and ignoble in his
           attitude"; "I think it a less evil that some criminals
           should escape than that the government should play an
           ignoble part"- Oliver Wendell Holmes, Jr. [ant: noble]
    2: not of the nobility; "of ignoble (or ungentle) birth";
       "untitled civilians" [syn: ignoble, ungentle, untitled]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "ignoble":
   abhorrent, abject, abominable, base, base-minded, baseborn,
   beastly, beggarly, below contempt, beneath contempt, coarse,
   common, contemptible, crude, derogatory, despicable, detestable,
   discreditable, disgusting, dishonorable, disreputable, execrable,
   fetid, forbidding, foul, fulsome, gross, hateful, heinous, homely,
   humble, ignominious, infamous, inferior, inglorious, loathsome,
   low, low-minded, lowborn, lowly, malodorous, mean, mephitic,
   miasmal, miasmic, modest, nasty, nauseating, noisome, notorious,
   noxious, objectionable, obnoxious, obscene, odious, offensive,
   ordinary, peasant, plain, plebeian, poor, popular, rebarbative,
   repellent, repugnant, repulsive, revolting, scrubby, scurvy, seamy,
   servile, shady, sickening, simple, sordid, sorry, stinking,
   unpraiseworthy, unrespectable, unsavory, unwashed, vile, vulgar,
   wretched