The Collaborative International Dictionary of English v.0.48:

Ignore \Ig*nore"\, v. t. [imp. & p. p. Ignored; p. pr. & vb.
   n. Ignoring.] [L. ignorare; pref. in- not + the root of
   gnarus knowing, noscere to become acquainted with. See
   Know, and cf. Narrate.]
   1. To be ignorant of or not acquainted with. [Archaic]
      [1913 Webster]

            Philosophy would solidly be established, if men
            would more carefully distinguish those things that
            they know from those that they ignore. --Boyle.
      [1913 Webster]

   2. (Law) To throw out or reject as false or ungrounded; --
      said of a bill rejected by a grand jury for lack of
      evidence. See Ignoramus.
      [1913 Webster]

   3. Hence: To refuse to take notice of; to shut the eyes to;
      not to recognize; to disregard willfully and causelessly;
      as, to ignore certain facts; to ignore the presence of an
      objectionable person.
      [1913 Webster]

            Ignoring Italy under our feet,
            And seeing things before, behind.     --Mrs.
                                                  Browning.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ignore
    v 1: refuse to acknowledge; "She cut him dead at the meeting"
         [syn: ignore, disregard, snub, cut]
    2: bar from attention or consideration; "She dismissed his
       advances" [syn: dismiss, disregard, brush aside, brush
       off, discount, push aside, ignore]
    3: fail to notice [ant: mark, note, notice]
    4: give little or no attention to; "Disregard the errors" [syn:
       neglect, ignore, disregard]
    5: be ignorant of or in the dark about [ant: cognise,
       cognize, know]

Moby Thesaurus II by Grady Ward, 1.0:

181 Moby Thesaurus words for "ignore":
   abide with, abjure, accept, allow for, avoid, ban, bar, bar out,
   be big, be blind to, be caught napping, be caught out,
   be content with, be easy with, be inattentive, be neglectful,
   be negligent, be unwary, bear with, blink at, blockade,
   break the law, brook, brush aside, brush off, care naught for,
   chuck, chuck out, color, condone, connive at, contemn, contradict,
   count out, cut, cut dead, cut off, debar, decline, default, defy,
   deny, despise, digest, diminish, disapprove, discard, disclaim,
   discount, disdain, dismiss, disobey, disown, disregard, down, ease,
   eat, embargo, endure, evade, except, exclude, extenuate, fail,
   flout, forget, forswear, freeze out, give no heed, give the go-by,
   gloss over, go counter to, hear nothing, judge not, keep out,
   lapse, lean over backwards, leave out, leave unavenged, lessen,
   let go, let it go, let pass, let ride, let slide, let slip,
   listen to reason, live with, lock out, look right through,
   lose sight of, lose track of, make allowance for,
   make allowances for, make light of, make little of, mince, miss,
   mitigate, neglect, nod, not attend, not care for, not conform,
   not get involved, not heed, not keep, not listen, not mind,
   not notice, not observe, not think, not write off, omit, ostracize,
   overlook, overpass, palliate, pass by, pass over, pass up,
   pay no attention, pay no mind, pocket, pocket the affront,
   pooh-pooh, preclude, prohibit, push aside, rebuff, recant, refuse,
   refuse to acknowledge, refuse to consider, refuse to cooperate,
   refuse to recognize, regard with indulgence, reject, relegate,
   renounce, repel, repudiate, repulse, scoff at, scout,
   see both sides, see nothing, send to Coventry, set at defiance,
   set at naught, set naught by, shove away, shut out, sleep, slight,
   slur over, snub, soft-pedal, soften, spurn, stomach,
   suspend judgment, swallow, swallow an insult, taboo, take,
   take for granted, think little of, throw away, throw out, tolerate,
   transgress, turn aside provocation, turn away, turn out, varnish,
   view with indulgence, violate, waive, whitewash, wink at