noun

1. a belief not based on absolute certainty or positive knowledge but on what seems true, valid, or probable to one's own mind; judgment
2. an evaluation, impression, or estimation of the quality or worth of a person or thing
3. the formal judgment of an expert on a matter in which advice is sought
4. Law the formal statement by a judge, court referee, etc. of the law bearing on a case

Etymology: ME opinioun < OFr < L opinio < opinari, to think, akin to optare, to select, desire: see option