The Collaborative International Dictionary of English v.0.48:

Opinion \O*pin"ion\, v. t.
   To opine. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Opinion \O*pin"ion\, n. [F., from L. opinio. See Opine.]
   1. That which is opined; a notion or conviction founded on
      probable evidence; belief stronger than impression, less
      strong than positive knowledge; settled judgment in regard
      to any point of knowledge or action.
      [1913 Webster]

            Opinion is when the assent of the understanding is
            so far gained by evidence of probability, that it
            rather inclines to one persuasion than to another,
            yet not without a mixture of incertainty or
            doubting.                             --Sir M. Hale.
      [1913 Webster]

            I can not put off my opinion so easily. --Shak.
      [1913 Webster]

   2. The judgment or sentiment which the mind forms of persons
      or things; estimation.
      [1913 Webster]

            I have bought golden opinions from all sorts of
            people.                               --Shak.
      [1913 Webster]

            Friendship . . . gives a man a peculiar right and
            claim to the good opinion of his friend. --South.
      [1913 Webster]

            However, I have no opinion of those things. --Bacon.
      [1913 Webster]

   3. Favorable estimation; hence, consideration; reputation;
      fame; public sentiment or esteem. [Obs.]
      [1913 Webster]

            Thou hast redeemed thy lost opinion.  --Shak.
      [1913 Webster]

            This gained Agricola much opinion, who . . . had
            made such early progress into laborious . . .
            enterprises.                          --Milton.
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   4. Obstinacy in holding to one's belief or impression;
      opiniativeness; conceitedness. [Obs.] --Shak.
      [1913 Webster]

   5. (Law.) The formal decision, or expression of views, of a
      judge, an umpire, a counselor, or other party officially
      called upon to consider and decide upon a matter or point
      submitted.
      [1913 Webster]

   To be of opinion, to think; to judge.

   To hold opinion with, to agree with. [Obs.] --Shak.
      [1913 Webster]

   Syn: Sentiment; notion; persuasion; idea; view; estimation.
        See Sentiment.
        [1913 Webster]

WordNet (r) 3.0 (2006):

opinion
    n 1: a personal belief or judgment that is not founded on proof
         or certainty; "my opinion differs from yours"; "I am not of
         your persuasion"; "what are your thoughts on Haiti?" [syn:
         opinion, sentiment, persuasion, view, thought]
    2: a message expressing a belief about something; the expression
       of a belief that is held with confidence but not
       substantiated by positive knowledge or proof; "his opinions
       appeared frequently on the editorial page" [syn: opinion,
       view]
    3: a belief or sentiment shared by most people; the voice of the
       people; "he asked for a poll of public opinion" [syn: public
       opinion, popular opinion, opinion, vox populi]
    4: the legal document stating the reasons for a judicial
       decision; "opinions are usually written by a single judge"
       [syn: opinion, legal opinion, judgment, judgement]
    5: the reason for a court's judgment (as opposed to the decision
       itself) [syn: opinion, ruling]
    6: a vague idea in which some confidence is placed; "his
       impression of her was favorable"; "what are your feelings
       about the crisis?"; "it strengthened my belief in his
       sincerity"; "I had a feeling that she was lying" [syn:
       impression, feeling, belief, notion, opinion]

Moby Thesaurus II by Grady Ward, 1.0:

113 Moby Thesaurus words for "opinion":
   admonition, advice, advising, advocacy, affect, affectivity,
   analyzing, appraisal, appraisement, appraising, appreciation,
   apprehension, assessing, assessment, assumption, attitude, belief,
   brief, briefing, caution, caveat, climate of opinion,
   common belief, community sentiment, conceit, concept, conception,
   conclusion, conjecture, consensus gentium, consideration,
   consultation, conviction, council, counsel, direction, emotion,
   emotivity, estimate, estimation, ethos, evaluating, evaluation,
   evaluative criticism, exhortation, expostulation, eye, fancy,
   feeling, feeling tone, gauging, general belief, guidance,
   hortation, idea, image, imago, impression, instruction,
   intellectual object, judgement, judgment, lights, measurement,
   memory-trace, mental attitude, mental image, mental impression,
   mind, monition, mystique, notion, observation, parley, perception,
   personal judgment, persuasion, point of view, popular belief,
   position, posture, presumption, prevailing belief, proposal,
   psychology, public belief, public opinion, ranking, rating,
   reaction, recept, reckoning, recommendation, reflection,
   remonstrance, representation, sentiment, sight, speculation,
   stance, suggestion, supposition, theory, think, thinking, thought,
   valuation, valuing, view, viewpoint, warning, way of thinking,
   weighing



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

OPINION, evidence. An inference made, or conclusion drawn, by a witness from
facts known to him,
     2. In general a witness cannot be asked his opinion upon a particular
question, for he is called to speak of facts only. But to this general rule
there are exceptions; where matters of skill and judgment are involved, a
person competent, particularly to understand such matters, may be asked his
opinion, and it will be evidence. 4 Hill, 129; 1 Denio, 281; 2 Scam. 297; 2
N. H. Rep. 480; 2 Story, R. 421; see 8 W. & S. 61; 1 McMullan, 561 For
example, an engineer may be called to say what, in his opinion, is the cause
that a harbor has teen blocked up. 3 Dougl. R. 158; S. C. 26 Eng. C. L. Rep.
63; 1 Phil. Ev. 276; 4 T. R. 498. A ship builder may be asked his opinion on
a question of sea-worthiness. Peake, N. P. C. 25; 10 Bing. R. 57; 25 Eng.
Com. Law Rep. 28.
     3. Medical men are usually examined as to their judgment with regard to
the cause of a person's death, who has suffered by violence. Vide Death. Of
the sanity, 1 Addams, 244, or impotency, 3 Phillim. 14, of an individual.
Professional men are, however, confined to state facts and opinions within
the scope of their professions, and are not allowed to give opinions on
things of which the jury can as well judge. 5 Rogers' Rec. 26; 4 Wend. 320;
3 Fairf. 398; 3 Dana, 882; 1 Pennsyl. 161; 2 Halst. 244; 7 Vern. 161; 6
Rand. 704; 4 Yeates, 262; 9 Conn. 102; 3 N. H. Rep. 349; 5 H. & J. 488.
     4. The unwritten or common law of foreign countries may be proved by
the opinion of witnesses possessing professional skill. Story's Confl. of
Laws, 530; 1 Cranch, 12, 38; 2 Cranch, 236; 6 Pet Rep. 763; Pet. C. C. R.
225; 2 Wash. C. C. R. 175; Id. 1; 5 Wend. Rep. 375; 2 Id. 411; 3 Pick. Rep.
293; 4 Conn. R. 517; 6 Conn: R. 486; 4 Bibb R. 73; 2 Marsh. Rep. 609; 5
Harr. & John. 86; 1 Johns. Rep. 385; 3 Johns. Rep. 105; 14 Mass., R. 455; 6
Conn. R. 508; 1 Vern. R. 336; 15 Serg. & Rawle, 87; 1, Louis. R. 153; 3 Id.
53; Cranch, 274. Vide also 14 Serg. & Rawle, 137; 3 N. Hamp. R. 349; 3
Yeates, 527; 1 Wheel. C. C. Rep. 205; 6 Rand. R. 704; 2 Russ. on Cr. 623; 4
Camp. R. 155; Russ. & Ry. 456; 2 Esp. C. 58; Foreign Laws; 3 Phillim. R.
449; 1 Eccl. R. 291.



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

OPINION, practice. A declaration by a counsel to his client of what the law
is, according to his judgment, on a statement of facts submitted to him. The
paper upon which an opinion is written is, by a figure of speech, also
called an opinion.
     2. The counsel should as far as practicable give, 1. A direct and
positive opinion, meeting the point and effect of the question and
separately, if the questions proposed were properly divisible into several.
2. The reasons, succinctly stated, in support of such opinion. 3. A
reference to the statute, rule or decision on the subject. 4. When the facts
are susceptible of a small difference in the statement, a suggestion of the
probability of such variation. 5. When some, important fact is stated as
resting principally on the statement of the party interested, a suggestion
ought to be made to inquire how that fact is to be proved. 6. A suggestion
of the proper process or pleadings to be adopted. 7. A suggestion of what
precautionary measures ought to be adopted. As to the value of an opinion,
see 4 Penn, St. R. 28.



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

OPINION, judgment. A collection of reasons delivered by a judge for giving
the judgment he is about to pronounce the judgment itself is sometimes
called an opinion.
     2. Such an opinion ought to be a perfect syllogism, the major of which
should be the law; the minor, the fact to be decided and the consequence,
the judgment which declares that to be conformable or contrary to law.
     3. Opinions are judicial or extra-judicial; a judicial opinion is one
which is given on a matter which is legally brought before the judge for his
decision; an extra-judicial opinion, is one which although given in court,
is not necessary to the judgment. Vaughan, 382; 1 Hale's Hist. 141; and
whether given in or out of court, is no more than the prolatum of him who
gives it, and has no legal efficacy. 4 Penn. St. R. 28. Vide Reason.