For the breakfast dish consisting of eggs that have been beaten, cooked until set, and folded over, American publications prefer omelet, and this is the spelling recommended by most American English reference sources. In all other main varieties of English, the French spelling, omelette, is preferred.
These are the preferences shown in 21st-century edited writing, anyway. There’s no rule saying Americans can’t prefer the French spelling or that British writers can’t prefer the American one, and both spellings appear to varying degrees throughout the English-speaking world.
Omelet is not American in origin. The word has actually had several English spellings over the centuries—including aumulet, ammulet, omlet, and amelet, all found in the OED’s historical examples—and omelet first appeared as long ago as the early 17th century (before the U.S. existed). By the 19th century, however, much of the English-speaking world had settled on the French spelling. Americans went a different direction.
Outside the U.S.
But the findings suggest that if you have diabetes, you may want to swap sunny side up for a whites-only omelette. [Globe and Mail]
This recipe is delicious using soft rolls, thin omelette and super-thin slices of prosciutto or ham. [Stuff.co.nz]
As the old saying goes, you do not make omelette without breaking a few eggs. [Sydney Morning Herald]
He is like someone with an allergy to eggs, drawn against his will to the lovely, fluffy omelette of married life. [Daily Mail]
But hey, you can’t make a revolutionary labor omelet without breaking some eggs. [Los Angeles Times]
I’m going to order an omelet—and stand there to watch that you don’t begin by pouring a cup of oil into the pan. [Forbes]
The cook wore a plastic glove on his right hand only, which made for an interesting Michael Jackson effect, but also produced a bare-hand-on-my-cheese-omelet effect [Wall Street Journal]