" 

 :::::I am contending that every grammar guide and dictionary of American English I have checked shows ""American"" is an accepted demonyn while ""United States"" is only used as a noun. This has nothing to do with your ability to extrapolate a new word usage from the first part of a proper name.  Are you contending that your personal knowledge and expertise in American English is superior to publishing houses such as Houghton Mifflin, Merriam–Webster, Random House, and Simon & Schuster? ''''  "