is united states of america an empire?

I always thought you needed a monarch to be one of those. I guess a President is kinda close, but he doesn't have full control does he? (Although of course this does not include secret rulers of America, who may very well be one king)

Also unrelated, but I had to go through:

-Empire Magazine
-Empire Apartments
-Empire Cinema
-Empire Skateboards
-Empire Kitchens
-Empire Tavern
-Empire (2002) film.

before I got to a page about what empires actually are.