Can I use "US-American" to disambiguate "American"? If not, what can I use?

Based on this question, I wonder: as an alternative to USAian (which is very nonstandard) is it OK to use US-American to more clearly indicate "inhabitant of the USA"?

According to Google Ngram, this phrase has grown in usage since the 1960's.

The problem I'm trying to solve is that American can relate to either an inhabitant of the American continent(s), or an inhabitant of the United States of America. (In fact, the one Brazilian person I know does refer to himself as American, or at least would like to be able to do so.)

I'm looking for a word that specifically means "inhabitant of the United States of America".

I can see that in German, 'US-Amerikaner' is certainly not uncommon (see e.g. Wikipedia). Also, see also the Wikipedia article Names for United States citizens.

Alternatively, if it turns out that "American" always means an inhabitant of the USA, what word can be used for inhabitants of the continent?

I did a search on Google for US-American and found relatively little use of that phrase. Couple that with years as a native speaker and I can say that it is not "Standard" in my experience. That being said, it is understandable, and maybe even appropriate when you need a clear distinction from others in this hemisphere.

SUPPLEMENT:
TecBrat has, I believe, answered your explicit question entirely adequately; I add this to address your underlying question

[What is] a word [other than American] meaning "inhabitant of the United States of America"?

There is no such word in common acceptance. American has squatter's rights on that particular plot of linguistic domain, and owns bigger guns than anybody who wants to eject him.

So I recommend giving up the search for one word. When you want to discriminate citizens, denizens or speakers of the United States† from other Americans, just stick US in front of the noun: US citizens, US denizens, US speakers. It's not what you want, but it works.

†which country, by the way, includes a sizeable group of islands in the middle of the Pacific Ocean, well removed from the American continents

Since gerrit noted that "US-American" is not uncommon in Germany, I want to confirm that the expression is perfectly valid in this context. I work in an American Studies department at a German university, and I see "US-American" (or "US-Amerikaner") used all the time in scholarly writing in order to distinguish Americans from the United States from Americans from Canada and Latin America. Whether this is common usage in the US, Canada, or Latin America is a totally different issue. I just wanted to say that the answer to the original question is yes, you can use "US-American," but the legitimacy of this usage depends on national context.

Several reasons exist for the rare, and potentially not appropriate, usage of "US-Americans":

• the USA was the first country in the Americas to embrace 'being America' - as an invented nation of colonists. Other nations were, by contrast, active in the preservation of the root culture of locale populace (as allowed by Church and Colonial State).
• Canadians rarely use the term "North Americans" since the name of their country has no confusion with other countries in the Americas. Thus, US citizens can rather-safely be referred to as North Americans
• Mexico, today, is not in the northern americas, and never was given the historical use of Mesoamerican.
• As a melting pot nation, the USA seems to prefer to formally disavow of homeland-base prefixes (African American, Asian American, Irish American, Polish American, etc) on the grounds that they paint a fractured picture — except during national speeches where the togetherness of these peoples dissolves any pre-melting-pot ideas.

edit: I have completely revised my answer after realizing the OP asked about people-nomenclature, not language-nomenclature.