The Collaborative International Dictionary of English v.0.48:

Omit \O*mit"\, v. t. [imp. & p. p. Omitted; p. pr. & vb. n.
   Omitting.] [L. omittere, omissum; ob (see Ob- + mittere
   to cause to go, let go, send. See Mission.]
   1. To let go; to leave unmentioned; not to insert or name; to
      drop.
      [1913 Webster]

            These personal comparisons I omit.    --Bacon.
      [1913 Webster]

   2. To forbear or fail to perform or to make use of; to leave
      undone; to neglect; to pass over.
      [1913 Webster]

            Her father omitted nothing in her education that
            might make her the most accomplished woman of her
            age.                                  --Addison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

omit
    v 1: prevent from being included or considered or accepted; "The
         bad results were excluded from the report"; "Leave off the
         top piece" [syn: exclude, except, leave out, leave
         off, omit, take out] [ant: include]
    2: leave undone or leave out; "How could I miss that typo?";
       "The workers on the conveyor belt miss one out of ten" [syn:
       neglect, pretermit, omit, drop, miss, leave out,
       overlook, overleap] [ant: attend to, take to heart]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "omit":
   abandon, abbreviate, abridge, ban, bar, bar out, blink at,
   blockade, blot out, blue-pencil, bowdlerize, cancel, censor,
   count out, cross out, cut, cut off, cut out, debar, dele, delete,
   discount, disregard, edit, edit out, embargo, eradicate, erase,
   except, exclude, expunge, expurgate, fail, forget, freeze out,
   goldbrick, goof off, ignore, jump, keep out, kill, leave,
   leave loose ends, leave out, leave undone, let alone, let be,
   let dangle, let go, let slide, lock out, malinger, miss, neglect,
   obliterate, ostracize, overlook, overpass, pass over, pass up,
   preclude, pretermit, procrastinate, prohibit, reject, relegate,
   repudiate, rescind, rub out, send to Coventry, shirk, shut out,
   skip, slack, slight, strike, strike off, strike out, taboo, trifle,
   void