The Collaborative International Dictionary of English v.0.48:

Admonish \Ad*mon"ish\, v. t. [imp. & p. p. Admonished; p. pr.
   & vb. n. Admonishing.] [OE. amonesten, OF. amonester, F.
   admonester, fr. a supposed LL. admonesstrare, fr. L. admonere
   to remind, warn; ad + monere to warn. See Monition.]
   1. To warn or notify of a fault; to reprove gently or kindly,
      but seriously; to exhort. "Admonish him as a brother." --2
      Thess. iii. 15.
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   2. To counsel against wrong practices; to cation or advise;
      to warn against danger or an offense; -- followed by of,
      against, or a subordinate clause.
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            Admonishing one another in psalms and hymns. --Col.
                                                  iii. 16.
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            I warned thee, I admonished thee, foretold
            The danger, and the lurking enemy.    --Milton.
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   3. To instruct or direct; to inform; to notify.
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            Moses was admonished of God, when he was about to
            make the tabernacle.                  --Heb. viii.
                                                  5.
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WordNet (r) 3.0 (2006):

admonish
    v 1: admonish or counsel in terms of someone's behavior; "I
         warned him not to go too far"; "I warn you against false
         assumptions"; "She warned him to be quiet" [syn: warn,
         discourage, admonish, monish]
    2: warn strongly; put on guard [syn: caution, admonish,
       monish]
    3: take to task; "He admonished the child for his bad behavior"
       [syn: admonish, reprove]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "admonish":
   advise, alert, bring to book, call down, call to account, caution,
   charge, chastise, chide, correct, cry havoc, cry out against,
   daunt, dissuade, encourage, enjoin, exhort, expostulate, forewarn,
   frighten off, give fair warning, give notice, give warning,
   have words with, incite, induce, intimidate, issue a caveat,
   issue an ultimatum, kid out of, lecture, lesson, move, notify,
   objurgate, persuade, preach, prompt, rate, rebuke, remonstrate,
   reprehend, reprimand, reproach, reprove, scold, set down,
   set straight, sound the alarm, spank, straighten out, take down,
   take to task, talk out of, threaten, tick off, tip, tip off,
   unpersuade, upbraid, urge, utter a caveat, warn, warn against