See sense 3:
Main Entry: 1American
Pronunciation: \-mer--kn, -mr-, -me-r-\
1 : an American Indian of North America or South America
2 : a native or inhabitant of North America or South America
3 : a citizen of the United States
4 : american english
Sense 4 is a particularly scary development, however.
Doesn't count. You're quoting a USAian dictionary.
I have a theory that it's impossible to prove anything, but I can't prove it.