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.