The Collaborative International Dictionary of English v.0.48:

Abet \A*bet"\, n. [OF. abet, fr. abeter.]
   Act of abetting; aid. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Abet \A*bet"\, v. t. [imp. & p. p. Abetted; p. pr. & vb. n.
   Abetting.] [OF. abeter; a (L. ad) + beter to bait (as a
   bear), fr. Icel. beita to set dogs on, to feed, originally,
   to cause to bite, fr. Icel. b[imac]ta to bite, hence to bait,
   to incite. See Bait, Bet.]
   1. To instigate or encourage by aid or countenance; -- used
      in a bad sense of persons and acts; as, to abet an
      ill-doer; to abet one in his wicked courses; to abet vice;
      to abet an insurrection. "The whole tribe abets the
      villany." --South.
      [1913 Webster]

            Would not the fool abet the stealth,
            Who rashly thus exposed his wealth?   --Gay.
      [1913 Webster]

   2. To support, uphold, or aid; to maintain; -- in a good
      sense. [Obs.].

            Our duty is urged, and our confidence abetted.
                                                  --Jer. Taylor.
      [1913 Webster]

   3. (Law) To contribute, as an assistant or instigator, to the
      commission of an offense.
      [1913 Webster]

   Syn: To incite; instigate; set on; egg on; foment; advocate;
        countenance; encourage; second; uphold; aid; assist;
        support; sustain; back; connive at.
        [1913 Webster]

WordNet (r) 3.0 (2006):

abet
    v 1: assist or encourage, usually in some wrongdoing

Moby Thesaurus II by Grady Ward, 1.0:

82 Moby Thesaurus words for "abet":
   advance, advocate, aid, aid and abet, approve of, ask for, assist,
   avail, bail out, bear a hand, befriend, benefit, comfort, condone,
   countenance, do for, do good, doctor, ease, egg, egg on, embolden,
   encourage, endorse, exhort, favor, feed, foment, foster, further,
   give a boost, give a hand, give a lift, give encouragement,
   give help, go for, goad, hearten, help, help out, incite,
   instigate, invite, keep in countenance, lend a hand, lend one aid,
   nourish, nurture, prod, proffer aid, promote, protect, provoke,
   raise, rally, reclaim, redeem, relieve, remedy, render assistance,
   rescue, restore, resuscitate, revive, sanction, save, second, set,
   set on, set up, shine upon, smile upon, spur, stead, stir up,
   subscribe, succor, support, take in tow, uphold, urge, whip up