n.
  - a view or judgement not necessarily based on fact or knowledge. ▸the beliefs or views of a large number of people. ▸an estimation of quality or worth: ![]()  he had a high opinion of himself. 
- Law  a formal statement of reasons for a judgement given. ▸a barrister's advice on the merits of a case. 
Phrase
  
    - be of the opinion that
 believe or maintain that.
- a matter of opinion
 something not capable of being proven either way.
 
  Etymology
  ME: via OFr. from L. opinio(n-), from the stem of opinari ‘think, believe’.