noun.
A person who comments; especially someone who is paid to give his/her opinions in the media about current affairs, sports, etc.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
an expert who observes and comments on something
noun.
a writer who reports and analyzes events of the day
Word Usage
"I don't know who this commentator is (other than the guy that takes over for espn3 in the evening in Paris), but this is what happens when you're commentating on a match you don't care about and you're all alone in the booth."