The Collaborative International Dictionary of English v.0.48:

Admonition \Ad`mo*ni"tion\, n. [OE. amonicioun, OF. amonition,
   F. admonition, fr. L. admonitio, fr. admonere. See
   Admonish.]
   Gentle or friendly reproof; counseling against a fault or
   error; expression of authoritative advice; friendly caution
   or warning.
   [1913 Webster]

   Syn: Admonition, Reprehension, Reproof.

   Usage: Admonition is prospective, and relates to moral
          delinquencies; its object is to prevent further
          transgression. Reprehension and reproof are
          retrospective, the former being milder than the
          latter. A person of any age or station may be liable
          to reprehension in case of wrong conduct; but reproof
          is the act of a superior. It is authoritative
          fault-finding or censure addressed to children or to
          inferiors.
          [1913 Webster]

WordNet (r) 3.0 (2006):

admonition
    n 1: cautionary advice about something imminent (especially
         imminent danger or other unpleasantness); "a letter of
         admonition about the dangers of immorality"; "the warning
         was to beware of surprises"; "his final word of advice was
         not to play with matches" [syn: admonition, monition,
         warning, word of advice]
    2: a firm rebuke [syn: admonition, admonishment, monition]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "admonition":
   admonishment, advice, advising, advocacy, alarm, briefing,
   castigation, caution, cautioning, caveat, chastisement, chiding,
   consultation, correction, council, counsel, determent, deterrence,
   deterrent example, direction, example, exhortation, expostulation,
   final notice, final warning, forewarning, frightening off,
   guidance, hint, hortation, idea, instruction, intimidation,
   lecture, lesson, monition, moral, notice, notification,
   object lesson, objurgation, opinion, parley, proposal, rap, rating,
   rebuke, recommendation, remonstrance, reprehension, reprimand,
   reproach, reprobation, reproof, reproval, scolding, sermon,
   spanking, suggestion, talking out of, thought, threat, tip-off,
   ultimatum, upbraiding, verbum sapienti, warning, warning piece,
   wig



Bouvier's Law Dictionary, Revised 6th Ed (1856):

ADMONITION. A reprimand from a judge to a person accused, on being
discharged, warning him of the consequences of his conduct, and intimating
to him, that should he be guilty of the same fault for which he has been
admonished, he will be punished with greater severity. Merlin, Repert. h.t.
     2. The admonition was authorized by the civil law, as a species of
punishment for slight misdemeanors. Vide Reprimand



The Devil's Dictionary (1881-1906):

ADMONITION, n.  Gentle reproof, as with a meat-axe.  Friendly warning.

    Consigned by way of admonition,
    His soul forever to perdition.
                                                              Judibras