opinionate (v.)

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.).

verbal suffix for Latin verbs in -are, identical with -ate (1). Old English commonly made verbs from adjectives by adding a verbal ending to the word (such as gnornian "be sad, mourn," gnorn "sad, depressed"), but as the inflections wore off English words in late Old and early Middle English, there came to be no difference between the adjective and the verb in dry, empty, warm, etc. Thus accustomed to the identity of adjectival and verbal forms of a word, the English, when they began to expand their Latin-based vocabulary after c. 1500, simply made verbs from Latin past-participial adjectives without changing their form (such as aggravate, substantiate) and it became the custom that Latin verbs were Englished from their past participle stems.

c. 1600, "stiff in adhering to preconceived notions," past-participle adjective from opinionate. Now seemingly with more a sense of "obstinate in asserting one's opinions." Earlier words included opinioned (1580s) "attached to particular opinions;" opiniated (1590s); opinative (early 15c.) "founded only on personal opinion" (from Old French and Medieval Latin). Related: Opinonatedness.