First, is "pro" an abbreviated form of "professional"? If yes, does "Pro American" mean "Professional American"?
Here are the three meanings of pro:
In your example, pro-American is an adjective (pro functions as a preposition here), and as such, it should always be hyphenated. Example: His views are definitely pro-American. On the other hand, pro America is an adverbial phrase and it should not be hyphenated. Example: The Non-Aligned Movement has never been pro America.
No, in the usage you describe, pro means in favor of or a proponent of. I believe the etymology is simply that pro is Latin meaning for.
So if someone is Pro American, it would mean that they have a favorable opinion of America in some context.
Edit: I'll note the opposite is normally anti. Anti-American sentiments would be those that are unfavorable to America
protected by RegDwigнt♦ Mar 21 '13 at 14:27
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