Meaning of "pro" before a noun

Solution 1:

Here are the three meanings of pro:

• (noun) professional. Example: Don't mess with me. I'm a pro!

• (noun) advantage. Used mainly within the context of pros and cons (advantages and disadvantages). Example: The pros of democratic governance far outweigh the cons.

• (preposition/adverb) in support of. Example: I'm a pro-choice activist.

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.

Solution 2:

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