The Collaborative International Dictionary of English v.0.48:

Dictum \Dic"tum\, n.; pl. L. Dicta, E. Dictums. [L., neuter
   of dictus, p. p. of dicere to say. See Diction, and cf.
   Ditto.]
   1. An authoritative statement; a dogmatic saying; an
      apothegm.
      [1913 Webster]

            A class of critical dicta everywhere current. --M.
                                                  Arnold.
      [1913 Webster]

   2. (Law)
      (a) A judicial opinion expressed by judges on points that
          do not necessarily arise in the case, and are not
          involved in it.
      (b) (French Law) The report of a judgment made by one of
          the judges who has given it. --Bouvier.
      (c) An arbitrament or award.
          [1913 Webster]

WordNet (r) 3.0 (2006):

dictum
    n 1: an authoritative declaration [syn: pronouncement,
         dictum, say-so]
    2: an opinion voiced by a judge on a point of law not directly
       bearing on the case in question and therefore not binding
       [syn: obiter dictum, dictum]

Moby Thesaurus II by Grady Ward, 1.0:

162 Moby Thesaurus words for "dictum":
   Parthian shot, a priori truth, action, adage, address, affirmance,
   affirmation, allegation, ana, analects, announcement, annunciation,
   answer, aphorism, apostrophe, apothegm, appointment, assertion,
   asseveration, averment, avouchment, avowal, award, axiom, brevet,
   brocard, bull, byword, canon, catchword, code, collected sayings,
   commandment, comment, conclusion, condemnation, consideration,
   convention, crack, creed, current saying, decision, declaration,
   decree, decree-law, decreement, decretal, decretum, deliverance,
   determination, diagnosis, dictate, diktat, distich, doom, edict,
   edictum, enunciation, epigram, exclamation, expression, fiat,
   finding, form, formula, general principle, gnome, golden rule,
   golden saying, greeting, guideline, guiding principle, imperative,
   interjection, ipse dixit, law, manifesto, maxim, mention, mitzvah,
   moral, mot, motto, norm, note, observation, oracle, order,
   ordinance, ordonnance, phrase, pithy saying, position,
   position paper, positive declaration, postulate, precedent,
   precept, predicate, predication, prescript, principium, principle,
   proclamation, profession, prognosis, pronouncement, pronunciamento,
   proposition, protest, protestation, proverb, proverbial saying,
   proverbs, question, reflection, regulation, remark, rescript,
   resolution, rubric, rule, ruling, saw, say, say-so, saying,
   self-evident truth, senatus consult, senatus consultum, sentence,
   sententious expression, settled principle, sloka, stance, stand,
   standard, statement, stock saying, subjoinder, sutra, teaching,
   tenet, text, theorem, thought, truism, truth, ukase,
   universal truth, utterance, verdict, verse, vouch, wisdom,
   wisdom literature, wise saying, witticism, word, words of wisdom,
   working principle, working rule



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

DICTUM, practice. Dicta are judicial opinions expressed by the judges on
points that do not necessarily arise in the case.
     2. Dicta are regarded as of little authority, on account of the manner
in which they are delivered; it frequently happening that they are given
without much reflection, at the bar, without previous examination. "If,"
says Huston, J., in Frants v. Brown, 17 Serg. & Rawle, 292, "general dicta
in cases turning on special circumstances are to be considered as
establishing the law, nothing is yet settled, or can be long settled." "What
I have said or written, out of the case trying," continues the learned
judge, "or shall say or write, under such circumstances, maybe taken as my
opinion at the time, without argument or full consideration; but I will
never consider myself bound by it when the point is fairly trying and fully
argued and considered. And I protest against any person considering such
obiter dicta as my deliberate opinion." And it was considered by another
learned judge. Mr. Baron Richards, to be a "great misfortune that dicta are
taken down from judges, perhaps incorrectly, and then cited as absolute
propositions." 1 Phillim. Rep. 1406; S. C. 1 Eng. Ecc. R. 129; Ram. on
Judgm. ch. 5, p. 36; Willes' Rep. 666; 1 H. Bl. 53-63; 2 Bos. & P. 375; 7 T.
R. 287; 3 B. & A. 341; 2 Bing. 90. The doctrine of the courts of France on
this subject is stated in 11 Toull. 177, n. 133.
     3. In the French law, the report of a judgment made by one of the
judges who has given it, is called the dictum. Poth. Proc. Civ. partie 1, c.
5, art. 2.