a view or judgment formed about a particular matter
I'm of the opinion that he's lying
a belief that is not supported by positive knowledge
a generally held view
a formal expression by an expert of his or her professional judgment or advice, esp a barrister's written advice to a client
chiefly NAmer a formal expression of the principles on which a legal decision is based
matter of opinion
something that about which people differ and which cannot be decided objectively or proved conclusively one way or the other
[Middle English via French from Latin opinion-, opinio, from opinari to have an opinion]