opinion (n.)

early 14c., opinioun, "a judgment formed or a conclusion reached, especially one based on evidence that does not produce knowledge or certainty," from Old French opinion "opinion, view, judgements founded upon probabilities" (12c.), from Latin opinionem (nominative opinio) "opinion, conjecture, fancy, belief, what one thinks; appreciation, esteem," from stem of opinari "think, judge, suppose, opine," from PIE *op- (2) "to choose" (see option).

Where there is much desire to learn, there of necessity will be much arguing, much writing, many opinions; for opinion in good men is but knowledge in the making. [Milton, "Areopagitica"]

The word always has tended toward "a judgment or view regarded as influenced more by sentiment or feeling than reason." The meaning "formal statement by a judge or other professional" is from late 15c. The specific sense of "the estimate one forms of the character or qualities of persons or things" is by c. 1500. Public opinion, "the prevailing view in a given community on any matter of general interest or concern," is by 1735.

Middle English, perhaps reflecting the era's concern for obtaining knowledge through learned disputation, had opinional "characterized by likelihood rather than certainty" and opinial "based on probable but not certain evidence" (both mid-15c.).

Others are reading

Definitions of opinion

opinion (n.)
a personal belief or judgment that is not founded on proof or certainty;
my opinion differs from yours
Synonyms: sentiment / persuasion / view / thought
opinion (n.)
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
Synonyms: view
opinion (n.)
a belief or sentiment shared by most people; the voice of the people;
he asked for a poll of public opinion
Synonyms: public opinion / popular opinion / vox populi
opinion (n.)
the legal document stating the reasons for a judicial decision;
opinions are usually written by a single judge
Synonyms: legal opinion / judgment / judgement
opinion (n.)
the reason for a court's judgment (as opposed to the decision itself);
Synonyms: ruling
opinion (n.)
a vague idea in which some confidence is placed;
Synonyms: impression / feeling / belief / notion