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.
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            I have bought golden opinions from all sorts of
            people.                               --Shak.
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            Friendship . . . gives a man a peculiar right and
            claim to the good opinion of his friend. --South.
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            However, I have no opinion of those things. --Bacon.
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   3. Favorable estimation; hence, consideration; reputation;
      fame; public sentiment or esteem. [Obs.]
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            Thou hast redeemed thy lost opinion.  --Shak.
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            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.
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   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.
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   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]