The verb opine is used when someone speaks up and expresses an opinion. You might opine that dogs are highly preferable to cats.
Whenever you have something to say about a subject, you have the option to opine about it or keep your mouth shut. Movie critics opine about the best films of the year, and kindergarten kids opine that they'd rather not take a nap. Opine can also describe what you suppose will happen, like when you opine that school lunches will improve because of the new cook. The Latin opinari, or have an opinion, is the root of opine.